2025-11-17
1437. Check If All 1's Are at Least Length K Places Away

Topic: Array
Difficulty: Easy

Problem:
Given an binary array nums and an integer k, return true if all 1's are at least k places away from each other, otherwise return false.

Example 1:

Image: https://assets.leetcode.com/uploads/2020/04/15/sample_1_1791.png

Input: nums = [1,0,0,0,1,0,0,1], k = 2
Output: true
Explanation: Each of the 1s are at least 2 places away from each other.

Example 2:

Image: https://assets.leetcode.com/uploads/2020/04/15/sample_2_1791.png

Input: nums = [1,0,0,1,0,1], k = 2
Output: false
Explanation: The second 1 and third 1 are only one apart from each other.

Constraints:

• 1 <= nums.length <= 10^5
• 0 <= k <= nums.length
• nums[i] is 0 or 1

2025-11-18
717. 1-bit and 2-bit Characters

Topic: Array
Difficulty: Easy

Problem:
We have two special characters:

• The first character can be represented by one bit 0.
• The second character can be represented by two bits (10 or 11).

Given a binary array bits that ends with 0, return true if the last character must be a one-bit character.

Example 1:

Input: bits = [1,0,0]
Output: true
Explanation: The only way to decode it is two-bit character and one-bit character.
So the last character is one-bit character.

Example 2:

Input: bits = [1,1,1,0]
Output: false
Explanation: The only way to decode it is two-bit character and two-bit character.
So the last character is not one-bit character.

Constraints:

• 1 <= bits.length <= 1000
• bits[i] is either 0 or 1.

2025-11-19
2154. Keep Multiplying Found Values by Two

Topic: Array, Hash Table, Sorting, Simulation
Difficulty: Easy

Problem:
You are given an array of integers nums. You are also given an integer original which is the first number that needs to be searched for in nums.

You then do the following steps:

1. If original is found in nums, multiply it by two (i.e., set original = 2 * original).
2. Otherwise, stop the process.
3. Repeat this process with the new number as long as you keep finding the number.

Return the final value of original.

Example 1:

Input: nums = [5,3,6,1,12], original = 3
Output: 24
Explanation: 
- 3 is found in nums. 3 is multiplied by 2 to obtain 6.
- 6 is found in nums. 6 is multiplied by 2 to obtain 12.
- 12 is found in nums. 12 is multiplied by 2 to obtain 24.
- 24 is not found in nums. Thus, 24 is returned.

Example 2:

Input: nums = [2,7,9], original = 4
Output: 4
Explanation:
- 4 is not found in nums. Thus, 4 is returned.

Constraints:

• 1 <= nums.length <= 1000
• 1 <= nums[i], original <= 1000

2025-11-20
757. Set Intersection Size At Least Two

Topic: Array, Greedy, Sorting
Difficulty: Hard

Problem:
You are given a 2D integer array intervals where intervals[i] = [start_i, end_i] represents all the integers from start_i to end_i inclusively.

A containing set is an array nums where each interval from intervals has at least two integers in nums.

• For example, if intervals = [[1,3], [3,7], [8,9]], then [1,2,4,7,8,9] and [2,3,4,8,9] are containing sets.

Return the minimum possible size of a containing set.

Example 1:

Input: intervals = [[1,3],[3,7],[8,9]]
Output: 5
Explanation: let nums = [2, 3, 4, 8, 9].
It can be shown that there cannot be any containing array of size 4.

Example 2:

Input: intervals = [[1,3],[1,4],[2,5],[3,5]]
Output: 3
Explanation: let nums = [2, 3, 4].
It can be shown that there cannot be any containing array of size 2.

Example 3:

Input: intervals = [[1,2],[2,3],[2,4],[4,5]]
Output: 5
Explanation: let nums = [1, 2, 3, 4, 5].
It can be shown that there cannot be any containing array of size 4.

Constraints:

• 1 <= intervals.length <= 3000
• intervals[i].length == 2
• 0 <= start_i < end_i <= 10^8