https://leetcode.com/problems/open-the-lock/description/

Steps to rotate 4-wheel 0000 -> target #medium #bfs #deque

https://leetcode.com/problems/minimum-height-trees/description/


Center of an acyclic graph #medium #graph #toposort

https://leetcode.com/problems/n-th-tribonacci-number/description/

`n`th Tribonacci number f(n + 3) = f(n) + f(n + 1) + f(n + 2) #easy

https://leetcode.com/problems/longest-ideal-subsequence/description/

Max length of less than k adjucent subsequence #medium #dynamic_programming

https://leetcode.com/problems/minimum-falling-path-sum-ii/description/

Min non-direct path top down in a 2D matrix #hard #dynamic_programming

https://leetcode.com/problems/freedom-trail/description/

Min steps to produce key by rotating ring #hard #dynamic_programming #recursion #hash_map

https://leetcode.com/problems/sum-of-distances-in-tree/description/

Sums of paths to each leafs in a tree #hard #dfs

https://leetcode.com/problems/minimum-number-of-operations-to-make-array-xor-equal-to-k/description/

Bit diff between k and nums xor #medium #bit_manipulation

https://leetcode.com/problems/number-of-wonderful-substrings/description/

Count substrings with at most one odd frequency #medium #bit_manipulation

https://leetcode.com/problems/reverse-prefix-of-word/description/

Reverse [..ch] prefix in string #easy

https://leetcode.com/problems/largest-positive-integer-that-exists-with-its-negative/description/

Max number that have its negative in array #easy #two_pointers

https://leetcode.com/problems/compare-version-numbers/description/

Compare version numbers #medium

https://leetcode.com/problems/boats-to-save-people/description/

Minimum total boats with at most 2 people & limit weight #medium #two_pointers #greedy

https://leetcode.com/problems/delete-node-in-a-linked-list/description/

Delete current node in a Linked List #medium

https://leetcode.com/problems/remove-nodes-from-linked-list/description/

Make a Linked List non-increasing #medium #linked_list

https://leetcode.com/problems/double-a-number-represented-as-a-linked-list/description/

Double the number as a Linked List #medium #linked_list

https://leetcode.com/problems/relative-ranks/description/

Convert results array to ranks array #easy #sorting

https://leetcode.com/problems/maximize-happiness-of-selected-children/description/

Sum of k maximums decreasing each step #medium #sorting #heap #quickselect

https://leetcode.com/problems/k-th-smallest-prime-fraction/description/

k`th `arr[i]/arr[j], i < j, arr[i] < arr[j] #medium #heap #binary_search

https://leetcode.com/problems/minimum-cost-to-hire-k-workers/description/

Min cost of k workers each doing quality[i] work for fair rate #hard #heap #sorting