2025-03-23
1976. Number of Ways to Arrive at Destination

Topic: Dynamic Programming, Graph, Topological Sort, Shortest Path
Difficulty: Medium

Problem:
You are in a city that consists of n intersections numbered from 0 to n - 1 with bi-directional roads between some intersections. The inputs are generated such that you can reach any intersection from any other intersection and that there is at most one road between any two intersections.

You are given an integer n and a 2D integer array roads where roads[i] = [u_i, v_i, time_i] means that there is a road between intersections u_i and v_i that takes time_i minutes to travel. You want to know in how many ways you can travel from intersection 0 to intersection n - 1 in the shortest amount of time.

Return the number of ways you can arrive at your destination in the shortest amount of time. Since the answer may be large, return it modulo 10^9 + 7.

Example 1:

Image: https://assets.leetcode.com/uploads/2025/02/14/1976_corrected.png

Input: n = 7, roads = [[0,6,7],[0,1,2],[1,2,3],[1,3,3],[6,3,3],[3,5,1],[6,5,1],[2,5,1],[0,4,5],[4,6,2]]
Output: 4
Explanation: The shortest amount of time it takes to go from intersection 0 to intersection 6 is 7 minutes.
The four ways to get there in 7 minutes are:
- 0 ➝ 6
- 0 ➝ 4 ➝ 6
- 0 ➝ 1 ➝ 2 ➝ 5 ➝ 6
- 0 ➝ 1 ➝ 3 ➝ 5 ➝ 6

Example 2:

Input: n = 2, roads = [[1,0,10]]
Output: 1
Explanation: There is only one way to go from intersection 0 to intersection 1, and it takes 10 minutes.

Constraints:

• 1 <= n <= 200
• n - 1 <= roads.length <= n * (n - 1) / 2
• roads[i].length == 3
• 0 <= u_i, v_i <= n - 1
• 1 <= time_i <= 10^9
• u_i != v_i
• There is at most one road connecting any two intersections.
• You can reach any intersection from any other intersection.

2025-03-24
3169. Count Days Without Meetings

Topic: Array, Sorting
Difficulty: Medium

Problem:
You are given a positive integer days representing the total number of days an employee is available for work (starting from day 1). You are also given a 2D array meetings of size n where, meetings[i] = [start_i, end_i] represents the starting and ending days of meeting i (inclusive).

Return the count of days when the employee is available for work but no meetings are scheduled.

Note: The meetings may overlap.

Example 1:

Input: days = 10, meetings = [5,7,1,3,9,10]

Output: 2

Explanation:

There is no meeting scheduled on the 4^th and 8^th days.

Example 2:

Input: days = 5, meetings = [2,4,1,3]

Output: 1

Explanation:

There is no meeting scheduled on the 5^th day.

Example 3:

Input: days = 6, meetings = [1,6]

Output: 0

Explanation:

Meetings are scheduled for all working days.

Constraints:

• 1 <= days <= 10^9
• 1 <= meetings.length <= 10^5
• meetings[i].length == 2
• 1 <= meetings[i][0] <= meetings[i][1] <= days

2025-03-25
3394. Check if Grid can be Cut into Sections

Topic: Array, Sorting
Difficulty: Medium

Problem:
You are given an integer n representing the dimensions of an n x n grid, with the origin at the bottom-left corner of the grid. You are also given a 2D array of coordinates rectangles, where rectangles[i] is in the form [start_x, start_y, end_x, end_y], representing a rectangle on the grid. Each rectangle is defined as follows:

• (start_x, start_y): The bottom-left corner of the rectangle.
• (end_x, end_y): The top-right corner of the rectangle.

Note that the rectangles do not overlap. Your task is to determine if it is possible to make either two horizontal or two vertical cuts on the grid such that:

• Each of the three resulting sections formed by the cuts contains at least one rectangle.
• Every rectangle belongs to exactly one section.

Return true if such cuts can be made; otherwise, return false.

Example 1:

Input: n = 5, rectangles = [1,0,5,2,0,2,2,4,3,2,5,3,0,4,4,5]

Output: true

Explanation:

Image: https://assets.leetcode.com/uploads/2024/10/23/tt1drawio.png

The grid is shown in the diagram. We can make horizontal cuts at y = 2 and y = 4. Hence, output is true.

Example 2:

Input: n = 4, rectangles = [0,0,1,1,2,0,3,4,0,2,2,3,3,0,4,3]

Output: true

Explanation:

Image: https://assets.leetcode.com/uploads/2024/10/23/tc2drawio.png

We can make vertical cuts at x = 2 and x = 3. Hence, output is true.

Example 3:

Input: n = 4, rectangles = [0,2,2,4,1,0,3,2,2,2,3,4,3,0,4,2,3,2,4,4]

Output: false

Explanation:

We cannot make two horizontal or two vertical cuts that satisfy the conditions. Hence, output is false.

Constraints:

• 3 <= n <= 10^9
• 3 <= rectangles.length <= 10^5
• 0 <= rectangles[i][0] < rectangles[i][2] <= n
• 0 <= rectangles[i][1] < rectangles[i][3] <= n
• No two rectangles overlap.

2025-03-26
2033. Minimum Operations to Make a Uni-Value Grid

Topic: Array, Math, Sorting, Matrix
Difficulty: Medium

Problem:
You are given a 2D integer grid of size m x n and an integer x. In one operation, you can add x to or subtract x from any element in the grid.

A uni-value grid is a grid where all the elements of it are equal.

Return the minimum number of operations to make the grid uni-value. If it is not possible, return -1.

Example 1:

Image: https://assets.leetcode.com/uploads/2021/09/21/gridtxt.png

Input: grid = [[2,4],[6,8]], x = 2
Output: 4
Explanation: We can make every element equal to 4 by doing the following: 
- Add x to 2 once.
- Subtract x from 6 once.
- Subtract x from 8 twice.
A total of 4 operations were used.

Example 2:

Image: https://assets.leetcode.com/uploads/2021/09/21/gridtxt-1.png

Input: grid = [[1,5],[2,3]], x = 1
Output: 5
Explanation: We can make every element equal to 3.

Example 3:

Image: https://assets.leetcode.com/uploads/2021/09/21/gridtxt-2.png

Input: grid = [[1,2],[3,4]], x = 2
Output: -1
Explanation: It is impossible to make every element equal.

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 10^5
• 1 <= m * n <= 10^5
• 1 <= x, grid[i][j] <= 10^4

2025-03-27
2780. Minimum Index of a Valid Split

Topic: Array, Hash Table, Sorting
Difficulty: Medium

Problem:
An element x of an integer array arr of length m is dominant if more than half the elements of arr have a value of x.

You are given a 0-indexed integer array nums of length n with one dominant element.

You can split nums at an index i into two arrays nums[0, ..., i] and nums[i + 1, ..., n - 1], but the split is only valid if:

• 0 <= i < n - 1
• nums[0, ..., i], and nums[i + 1, ..., n - 1] have the same dominant element.

Here, nums[i, ..., j] denotes the subarray of nums starting at index i and ending at index j, both ends being inclusive. Particularly, if j < i then nums[i, ..., j] denotes an empty subarray.

Return the minimum index of a valid split. If no valid split exists, return -1.

Example 1:

Input: nums = [1,2,2,2]
Output: 2
Explanation: We can split the array at index 2 to obtain arrays [1,2,2] and [2]. 
In array [1,2,2], element 2 is dominant since it occurs twice in the array and 2 * 2 > 3. 
In array [2], element 2 is dominant since it occurs once in the array and 1 * 2 > 1.
Both [1,2,2] and [2] have the same dominant element as nums, so this is a valid split. 
It can be shown that index 2 is the minimum index of a valid split.

Example 2:

Input: nums = [2,1,3,1,1,1,7,1,2,1]
Output: 4
Explanation: We can split the array at index 4 to obtain arrays [2,1,3,1,1] and [1,7,1,2,1].
In array [2,1,3,1,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 > 5.
In array [1,7,1,2,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 > 5.
Both [2,1,3,1,1] and [1,7,1,2,1] have the same dominant element as nums, so this is a valid split.
It can be shown that index 4 is the minimum index of a valid split.

Example 3:

Input: nums = [3,3,3,3,7,2,2]
Output: -1
Explanation: It can be shown that there is no valid split.

Constraints:

• 1 <= nums.length <= 10^5
• 1 <= nums[i] <= 10^9
• nums has exactly one dominant element.

2025-03-28
2503. Maximum Number of Points From Grid Queries

Topic: Array, Two Pointers, Breadth-First Search, Union Find, Sorting, Heap (Priority Queue), Matrix
Difficulty: Hard

Problem:
You are given an m x n integer matrix grid and an array queries of size k.

Find an array answer of size k such that for each integer queries[i] you start in the top left cell of the matrix and repeat the following process:

• If queries[i] is strictly greater than the value of the current cell that you are in, then you get one point if it is your first time visiting this cell, and you can move to any adjacent cell in all 4 directions: up, down, left, and right.
• Otherwise, you do not get any points, and you end this process.

After the process, answer[i] is the maximum number of points you can get. Note that for each query you are allowed to visit the same cell multiple times.

Return the resulting array answer.

Example 1:

Image: https://assets.leetcode.com/uploads/2025/03/15/image1.png

Input: grid = [[1,2,3],[2,5,7],[3,5,1]], queries = [5,6,2]
Output: [5,8,1]
Explanation: The diagrams above show which cells we visit to get points for each query.

Example 2:

Image: https://assets.leetcode.com/uploads/2022/10/20/yetgriddrawio-2.png

Input: grid = [[5,2,1],[1,1,2]], queries = [3]
Output: [0]
Explanation: We can not get any points because the value of the top left cell is already greater than or equal to 3.

Constraints:

• m == grid.length
• n == grid[i].length
• 2 <= m, n <= 1000
• 4 <= m * n <= 10^5
• k == queries.length
• 1 <= k <= 10^4
• 1 <= grid[i][j], queries[i] <= 10^6

2025-03-29
2818. Apply Operations to Maximize Score

Topic: Array, Math, Stack, Greedy, Sorting, Monotonic Stack, Number Theory
Difficulty: Hard

Problem:
You are given an array nums of n positive integers and an integer k.

Initially, you start with a score of 1. You have to maximize your score by applying the following operation at most k times:

• Choose any non-empty subarray nums[l, ..., r] that you haven't chosen previously.
• Choose an element x of nums[l, ..., r] with the highest prime score. If multiple such elements exist, choose the one with the smallest index.
• Multiply your score by x.

Here, nums[l, ..., r] denotes the subarray of nums starting at index l and ending at the index r, both ends being inclusive.

The prime score of an integer x is equal to the number of distinct prime factors of x. For example, the prime score of 300 is 3 since 300 = 2 * 2 * 3 * 5 * 5.

Return the maximum possible score after applying at most k operations.

Since the answer may be large, return it modulo 10^9 + 7.

Example 1:

Input: nums = [8,3,9,3,8], k = 2
Output: 81
Explanation: To get a score of 81, we can apply the following operations:
- Choose subarray nums[2, ..., 2]. nums[2] is the only element in this subarray. Hence, we multiply the score by nums[2]. The score becomes 1 * 9 = 9.
- Choose subarray nums[2, ..., 3]. Both nums[2] and nums[3] have a prime score of 1, but nums[2] has the smaller index. Hence, we multiply the score by nums[2]. The score becomes 9 * 9 = 81.
It can be proven that 81 is the highest score one can obtain.

Example 2:

Input: nums = [19,12,14,6,10,18], k = 3
Output: 4788
Explanation: To get a score of 4788, we can apply the following operations: 
- Choose subarray nums[0, ..., 0]. nums[0] is the only element in this subarray. Hence, we multiply the score by nums[0]. The score becomes 1 * 19 = 19.
- Choose subarray nums[5, ..., 5]. nums[5] is the only element in this subarray. Hence, we multiply the score by nums[5]. The score becomes 19 * 18 = 342.
- Choose subarray nums[2, ..., 3]. Both nums[2] and nums[3] have a prime score of 2, but nums[2] has the smaller index. Hence, we multipy the score by nums[2]. The score becomes 342 * 14 = 4788.
It can be proven that 4788 is the highest score one can obtain.

Constraints:

• 1 <= nums.length == n <= 10^5
• 1 <= nums[i] <= 10^5
• 1 <= k <= min(n * (n + 1) / 2, 10^9)

2025-03-30
763. Partition Labels

Topic: Hash Table, Two Pointers, String, Greedy
Difficulty: Medium

Problem:
You are given a string s. We want to partition the string into as many parts as possible so that each letter appears in at most one part. For example, the string "ababcc" can be partitioned into ["abab", "cc"], but partitions such as ["aba", "bcc"] or ["ab", "ab", "cc"] are invalid.

Note that the partition is done so that after concatenating all the parts in order, the resultant string should be s.

Return a list of integers representing the size of these parts.

Example 1:

Input: s = "ababcbacadefegdehijhklij"
Output: [9,7,8]
Explanation:
The partition is "ababcbaca", "defegde", "hijhklij".
This is a partition so that each letter appears in at most one part.
A partition like "ababcbacadefegde", "hijhklij" is incorrect, because it splits s into less parts.

Example 2:

Input: s = "eccbbbbdec"
Output: [10]

Constraints:

• 1 <= s.length <= 500
• s consists of lowercase English letters.

2025-03-31
2551. Put Marbles in Bags

Topic: Array, Greedy, Sorting, Heap (Priority Queue)
Difficulty: Hard

Problem:
You have k bags. You are given a 0-indexed integer array weights where weights[i] is the weight of the i^th marble. You are also given the integer k.

Divide the marbles into the k bags according to the following rules:

• No bag is empty.
• If the i^th marble and j^th marble are in a bag, then all marbles with an index between the i^th and j^th indices should also be in that same bag.
• If a bag consists of all the marbles with an index from i to j inclusively, then the cost of the bag is weights[i] + weights[j].

The score after distributing the marbles is the sum of the costs of all the k bags.

Return the difference between the maximum and minimum scores among marble distributions.

Example 1:

Input: weights = [1,3,5,1], k = 2
Output: 4
Explanation: 
The distribution [1],[3,5,1] results in the minimal score of (1+1) + (3+1) = 6. 
The distribution [1,3],[5,1], results in the maximal score of (1+3) + (5+1) = 10. 
Thus, we return their difference 10 - 6 = 4.

Example 2:

Input: weights = [1, 3], k = 2
Output: 0
Explanation: The only distribution possible is [1],[3]. 
Since both the maximal and minimal score are the same, we return 0.

Constraints:

• 1 <= k <= weights.length <= 10^5
• 1 <= weights[i] <= 10^9

2025-04-01
2140. Solving Questions With Brainpower

Topic: Array, Dynamic Programming
Difficulty: Medium

Problem:
You are given a 0-indexed 2D integer array questions where questions[i] = [points_i, brainpower_i].

The array describes the questions of an exam, where you have to process the questions in order (i.e., starting from question 0) and make a decision whether to solve or skip each question. Solving question i will earn you points_i points but you will be unable to solve each of the next brainpower_i questions. If you skip question i, you get to make the decision on the next question.

• For example, given questions = [[3, 2], [4, 3], [4, 4], [2, 5]]:
• If question 0 is solved, you will earn 3 points but you will be unable to solve questions 1 and 2.
• If instead, question 0 is skipped and question 1 is solved, you will earn 4 points but you will be unable to solve questions 2 and 3.

Return the maximum points you can earn for the exam.

Example 1:

Input: questions = [[3,2],[4,3],[4,4],[2,5]]
Output: 5
Explanation: The maximum points can be earned by solving questions 0 and 3.
- Solve question 0: Earn 3 points, will be unable to solve the next 2 questions
- Unable to solve questions 1 and 2
- Solve question 3: Earn 2 points
Total points earned: 3 + 2 = 5. There is no other way to earn 5 or more points.

Example 2:

Input: questions = [[1,1],[2,2],[3,3],[4,4],[5,5]]
Output: 7
Explanation: The maximum points can be earned by solving questions 1 and 4.
- Skip question 0
- Solve question 1: Earn 2 points, will be unable to solve the next 2 questions
- Unable to solve questions 2 and 3
- Solve question 4: Earn 5 points
Total points earned: 2 + 5 = 7. There is no other way to earn 7 or more points.

Constraints:

• 1 <= questions.length <= 10^5
• questions[i].length == 2
• 1 <= points_i, brainpower_i <= 10^5

2025-04-02
2873. Maximum Value of an Ordered Triplet I

Topic: Array
Difficulty: Easy

Problem:
You are given a 0-indexed integer array nums.

Return the maximum value over all triplets of indices (i, j, k) such that i < j < k. If all such triplets have a negative value, return 0.

The value of a triplet of indices (i, j, k) is equal to (nums[i] - nums[j]) * nums[k].

Example 1:

Input: nums = [12,6,1,2,7]
Output: 77
Explanation: The value of the triplet (0, 2, 4) is (nums[0] - nums[2]) * nums[4] = 77.
It can be shown that there are no ordered triplets of indices with a value greater than 77.

Example 2:

Input: nums = [1,10,3,4,19]
Output: 133
Explanation: The value of the triplet (1, 2, 4) is (nums[1] - nums[2]) * nums[4] = 133.
It can be shown that there are no ordered triplets of indices with a value greater than 133.

Example 3:

Input: nums = [1,2,3]
Output: 0
Explanation: The only ordered triplet of indices (0, 1, 2) has a negative value of (nums[0] - nums[1]) * nums[2] = -3. Hence, the answer would be 0.

Constraints:

• 3 <= nums.length <= 100
• 1 <= nums[i] <= 10^6

2025-04-03
2874. Maximum Value of an Ordered Triplet II

Topic: Array
Difficulty: Medium

Problem:
You are given a 0-indexed integer array nums.

Return the maximum value over all triplets of indices (i, j, k) such that i < j < k. If all such triplets have a negative value, return 0.

The value of a triplet of indices (i, j, k) is equal to (nums[i] - nums[j]) * nums[k].

Example 1:

Input: nums = [12,6,1,2,7]
Output: 77
Explanation: The value of the triplet (0, 2, 4) is (nums[0] - nums[2]) * nums[4] = 77.
It can be shown that there are no ordered triplets of indices with a value greater than 77.

Example 2:

Input: nums = [1,10,3,4,19]
Output: 133
Explanation: The value of the triplet (1, 2, 4) is (nums[1] - nums[2]) * nums[4] = 133.
It can be shown that there are no ordered triplets of indices with a value greater than 133.

Example 3:

Input: nums = [1,2,3]
Output: 0
Explanation: The only ordered triplet of indices (0, 1, 2) has a negative value of (nums[0] - nums[1]) * nums[2] = -3. Hence, the answer would be 0.

Constraints:

• 3 <= nums.length <= 10^5
• 1 <= nums[i] <= 10^6

2025-04-04
1123. Lowest Common Ancestor of Deepest Leaves

Topic: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree
Difficulty: Medium

Problem:
Given the root of a binary tree, return the lowest common ancestor of its deepest leaves.

Recall that:

• The node of a binary tree is a leaf if and only if it has no children
• The depth of the root of the tree is 0. if the depth of a node is d, the depth of each of its children is d + 1.
• The lowest common ancestor of a set S of nodes, is the node A with the largest depth such that every node in S is in the subtree with root A.

Example 1:

Image: https://s3-lc-upload.s3.amazonaws.com/uploads/2018/07/01/sketch1.png

Input: root = [3,5,1,6,2,0,8,null,null,7,4]
Output: [2,7,4]
Explanation: We return the node with value 2, colored in yellow in the diagram.
The nodes coloured in blue are the deepest leaf-nodes of the tree.
Note that nodes 6, 0, and 8 are also leaf nodes, but the depth of them is 2, but the depth of nodes 7 and 4 is 3.

Example 2:

Input: root = [1]
Output: [1]
Explanation: The root is the deepest node in the tree, and it's the lca of itself.

Example 3:

Input: root = [0,1,3,null,2]
Output: [2]
Explanation: The deepest leaf node in the tree is 2, the lca of one node is itself.

Constraints:

• The number of nodes in the tree will be in the range [1, 1000].
• 0 <= Node.val <= 1000
• The values of the nodes in the tree are unique.

Note: This question is the same as 865: <https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/>

2025-04-05
1863. Sum of All Subset XOR Totals

Topic: Array, Math, Backtracking, Bit Manipulation, Combinatorics, Enumeration
Difficulty: Easy

Problem:
The XOR total of an array is defined as the bitwise XOR of all its elements, or 0 if the array is empty.

• For example, the XOR total of the array [2,5,6] is 2 XOR 5 XOR 6 = 1.

Given an array nums, return the sum of all XOR totals for every subset of nums. 

Note: Subsets with the same elements should be counted multiple times.

An array a is a subset of an array b if a can be obtained from b by deleting some (possibly zero) elements of b.

Example 1:

Input: nums = [1,3]
Output: 6
Explanation: The 4 subsets of [1,3] are:
- The empty subset has an XOR total of 0.
- [1] has an XOR total of 1.
- [3] has an XOR total of 3.
- [1,3] has an XOR total of 1 XOR 3 = 2.
0 + 1 + 3 + 2 = 6

Example 2:

Input: nums = [5,1,6]
Output: 28
Explanation: The 8 subsets of [5,1,6] are:
- The empty subset has an XOR total of 0.
- [5] has an XOR total of 5.
- [1] has an XOR total of 1.
- [6] has an XOR total of 6.
- [5,1] has an XOR total of 5 XOR 1 = 4.
- [5,6] has an XOR total of 5 XOR 6 = 3.
- [1,6] has an XOR total of 1 XOR 6 = 7.
- [5,1,6] has an XOR total of 5 XOR 1 XOR 6 = 2.
0 + 5 + 1 + 6 + 4 + 3 + 7 + 2 = 28

Example 3:

Input: nums = [3,4,5,6,7,8]
Output: 480
Explanation: The sum of all XOR totals for every subset is 480.

Constraints:

• 1 <= nums.length <= 12
• 1 <= nums[i] <= 20

2025-04-06
368. Largest Divisible Subset

Topic: Array, Math, Dynamic Programming, Sorting
Difficulty: Medium

Problem:
Given a set of distinct positive integers nums, return the largest subset answer such that every pair (answer[i], answer[j]) of elements in this subset satisfies:

• answer[i] % answer[j] == 0, or
• answer[j] % answer[i] == 0

If there are multiple solutions, return any of them.

Example 1:

Input: nums = [1,2,3]
Output: [1,2]
Explanation: [1,3] is also accepted.

Example 2:

Input: nums = [1,2,4,8]
Output: [1,2,4,8]

Constraints:

• 1 <= nums.length <= 1000
• 1 <= nums[i] <= 2 * 10^9
• All the integers in nums are unique.

2025-04-07
416. Partition Equal Subset Sum

Topic: Array, Dynamic Programming
Difficulty: Medium

Problem:
Given an integer array nums, return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise.

Example 1:

Input: nums = [1,5,11,5]
Output: true
Explanation: The array can be partitioned as [1, 5, 5] and [11].

Example 2:

Input: nums = [1,2,3,5]
Output: false
Explanation: The array cannot be partitioned into equal sum subsets.

Constraints:

• 1 <= nums.length <= 200
• 1 <= nums[i] <= 100

2025-04-08
3396. Minimum Number of Operations to Make Elements in Array Distinct

Topic: Array, Hash Table
Difficulty: Easy

Problem:
You are given an integer array nums. You need to ensure that the elements in the array are distinct. To achieve this, you can perform the following operation any number of times:

• Remove 3 elements from the beginning of the array. If the array has fewer than 3 elements, remove all remaining elements.

Note that an empty array is considered to have distinct elements. Return the minimum number of operations needed to make the elements in the array distinct.

Example 1:

Input: nums = 1,2,3,4,2,3,3,5,7

Output: 2

Explanation:

• In the first operation, the first 3 elements are removed, resulting in the array [4, 2, 3, 3, 5, 7].
• In the second operation, the next 3 elements are removed, resulting in the array [3, 5, 7], which has distinct elements.

Therefore, the answer is 2.

Example 2:

Input: nums = 4,5,6,4,4

Output: 2

Explanation:

• In the first operation, the first 3 elements are removed, resulting in the array [4, 4].
• In the second operation, all remaining elements are removed, resulting in an empty array.

Therefore, the answer is 2.

Example 3:

Input: nums = 6,7,8,9

Output: 0

Explanation:

The array already contains distinct elements. Therefore, the answer is 0.

Constraints:

• 1 <= nums.length <= 100
• 1 <= nums[i] <= 100

2025-04-09
3375. Minimum Operations to Make Array Values Equal to K

Topic: Array, Hash Table
Difficulty: Easy

Problem:
You are given an integer array nums and an integer k.

An integer h is called valid if all values in the array that are strictly greater than h are identical.

For example, if nums = [10, 8, 10, 8], a valid integer is h = 9 because all nums[i] > 9 are equal to 10, but 5 is not a valid integer.

You are allowed to perform the following operation on nums:

• Select an integer h that is valid for the current values in nums.
• For each index i where nums[i] > h, set nums[i] to h.

Return the minimum number of operations required to make every element in nums equal to k. If it is impossible to make all elements equal to k, return -1.

Example 1:

Input: nums = 5,2,5,4,5, k = 2

Output: 2

Explanation:

The operations can be performed in order using valid integers 4 and then 2.

Example 2:

Input: nums = 2,1,2, k = 2

Output: -1

Explanation:

It is impossible to make all the values equal to 2.

Example 3:

Input: nums = 9,7,5,3, k = 1

Output: 4

Explanation:

The operations can be performed using valid integers in the order 7, 5, 3, and 1.

Constraints:

• 1 <= nums.length <= 100
• 1 <= nums[i] <= 100
• 1 <= k <= 100

2025-04-10
2999. Count the Number of Powerful Integers

Topic: Math, String, Dynamic Programming
Difficulty: Hard

Problem:
You are given three integers start, finish, and limit. You are also given a 0-indexed string s representing a positive integer.

A positive integer x is called powerful if it ends with s (in other words, s is a suffix of x) and each digit in x is at most limit.

Return the total number of powerful integers in the range [start..finish].

A string x is a suffix of a string y if and only if x is a substring of y that starts from some index (including 0) in y and extends to the index y.length - 1. For example, 25 is a suffix of 5125 whereas 512 is not.

Example 1:

Input: start = 1, finish = 6000, limit = 4, s = "124"
Output: 5
Explanation: The powerful integers in the range [1..6000] are 124, 1124, 2124, 3124, and, 4124. All these integers have each digit <= 4, and "124" as a suffix. Note that 5124 is not a powerful integer because the first digit is 5 which is greater than 4.
It can be shown that there are only 5 powerful integers in this range.

Example 2:

Input: start = 15, finish = 215, limit = 6, s = "10"
Output: 2
Explanation: The powerful integers in the range [15..215] are 110 and 210. All these integers have each digit <= 6, and "10" as a suffix.
It can be shown that there are only 2 powerful integers in this range.

Example 3:

Input: start = 1000, finish = 2000, limit = 4, s = "3000"
Output: 0
Explanation: All integers in the range [1000..2000] are smaller than 3000, hence "3000" cannot be a suffix of any integer in this range.

Constraints:

• 1 <= start <= finish <= 10^15
• 1 <= limit <= 9
• 1 <= s.length <= floor(log_10(finish)) + 1
• s only consists of numeric digits which are at most limit.
• s does not have leading zeros.

2025-04-11
2843. Count Symmetric Integers

Topic: Math, Enumeration
Difficulty: Easy

Problem:
You are given two positive integers low and high.

An integer x consisting of 2 * n digits is symmetric if the sum of the first n digits of x is equal to the sum of the last n digits of x. Numbers with an odd number of digits are never symmetric.

Return the number of symmetric integers in the range [low, high].

Example 1:

Input: low = 1, high = 100
Output: 9
Explanation: There are 9 symmetric integers between 1 and 100: 11, 22, 33, 44, 55, 66, 77, 88, and 99.

Example 2:

Input: low = 1200, high = 1230
Output: 4
Explanation: There are 4 symmetric integers between 1200 and 1230: 1203, 1212, 1221, and 1230.

Constraints:

• 1 <= low <= high <= 10^4

2025-04-12
3272. Find the Count of Good Integers

Topic: Hash Table, Math, Combinatorics, Enumeration
Difficulty: Hard

Problem:
You are given two positive integers n and k.

An integer x is called k-palindromic if:

• x is a palindrome.
• x is divisible by k.

An integer is called good if its digits can be rearranged to form a k-palindromic integer. For example, for k = 2, 2020 can be rearranged to form the k-palindromic integer 2002, whereas 1010 cannot be rearranged to form a k-palindromic integer.

Return the count of good integers containing n digits.

Note that any integer must not have leading zeros, neither before nor after rearrangement. For example, 1010 cannot be rearranged to form 101.

Example 1:

Input: n = 3, k = 5

Output: 27

Explanation:

Some of the good integers are:

• 551 because it can be rearranged to form 515.
• 525 because it is already k-palindromic.

Example 2:

Input: n = 1, k = 4

Output: 2

Explanation:

The two good integers are 4 and 8.

Example 3:

Input: n = 5, k = 6

Output: 2468

Constraints:

• 1 <= n <= 10
• 1 <= k <= 9