Web Reference: In-depth solution and explanation for LeetCode 18. 4Sum in Python, Java, C++ and more. Intuitions, example walk through, and complexity analysis. Better than official and forum solutions. Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that: a, b, c, and d are distinct. You may return the answer in any order. Example 1: Output: [[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]] Example 2: Output: [[2,2,2,2]] Constraints: any solutions. No comments yet. The two-pointer technique from 2Sum and 3Sum extends naturally to 4Sum. After sorting, we fix the first two elements with nested loops, then use two pointers to find pairs that complete the target sum.
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