Given an array of integers, check if the array contains any duplicates.

ReadGiven a list of distinct integers, find all the possible combinations which sums up to a target.

ReadGiven a positive integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order.

ReadGiven a string, remove minimum number of parentheses to make it balanced.

ReadGiven root of a binary tree, check if it is balanced or not.

ReadGiven the root to a binary search tree, find the second largest node in the tree.

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