LeetCode 3045. Count Prefix and Suffix Pairs II

Using trie tree and z-algorithm to find prefix and suffix.

LeetCode 126. Word Ladder II

To solve the problem, we can use a combination of BFS and backtracking.

LeetCode 23. Merge k Sorted Lists

To merge k sorted linked lists efficiently, we can use a Min Heap data structure.

LeetCode 124. Binary Tree Maximum Path Sum

To find the maximum path sum in a binary tree, we can use a recursive approach. The idea is to traverse the tree in a bottom-up manner and calculate the maximum path sum for each node.

LeetCode 30. Substring with Concatenation of All Words

Because all the words are the same length, we can use hash map to check for substring from index i to index i +word length * words number.

LeetCode 42. Trapping Rain Water

We can calculate the water amount by columns. For position i, the water it can contains is based on the left max height column and the right max height columns.

LeetCode 135. Candy

This problem can be see as finding peak and valley. And we need to start checking the peak in order to remove the redundant count.

LeetCode 22. Generate Parentheses

We can get the n pairs of parentheses by combining the x pairs with n-1-x pairs then combine with one pair "()".

LeetCode 5. Longest Palindromic Substring

Solve using three ways.

LeetCode 19. Remove Nth Node From End of List

Use two pointers, let them always have a distance of n, so when right pointer reach the end, the left pointer is the last nth node.

LeetCode 301. Remove Invalid Parentheses

Using DFS method to check each possible remove.

LeetCode 279. Perfect Squares

Every natural number can be represented as a sum of four non-negative integer squares. That is, the squares form an additive basis of order four