Two Sum

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution, and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2,7,11,15], target = 9 Output: [0,1] Explanation: Because …

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Valid Mountain Array

Given an array of integers arr, return true if and only if it is a valid mountain array. Recall that arr is a mountain array if and only if: arr.length >= 3 There exists some i with 0 < i < arr.length – 1 such that: arr[0] < arr[1] < … < arr[i – 1] < arr[i] arr[i] > arr[i + 1] …

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DI String Match

A permutation perm of n + 1 integers of all the integers in the range [0, n] can be represented as a string s of length n where: s[i] == ‘I’ if perm[i] < perm[i + 1], and s[i] == ‘D’ if perm[i] > perm[i + 1]. Given a string s, reconstruct the permutation perm and return it. If there are multiple valid permutations perm, return any of them. …

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