LeetCode (Algorithms#16) ‒ 3Sum Closest

Problem

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Example:

    For example, given array S = {-1 2 1 -4}, and target = 1.

    The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Solution

This problem is identical to 3Sum. The difference being, instead of returning all sums, we return the (first) closest sum to the target. This simplification results in maintaining a solution with minimum distance to the target, mind in the code below, instead of checking for equivalence with the target and storing in a list.

Time complexity: $O(n^2)$
Space complexity: $O(1)$
Runtime: 18 ms (96.18%)

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public int threeSumClosest(int[] nums, int target) { if (nums==null || nums.length < 3) return 0; Arrays.sort(nums); // System.out.println(Arrays.toString(nums)); int l, r, v, len=nums.length, res=0, mind=Integer.MAX_VALUE; for (int i=0; i<len-1; i++) { if (i>0 && nums[i-1]==nums[i]) continue; l = i+1; r = len-1; while (l < r) { v = nums[i]+nums[l]+nums[r]; if (Math.abs(v-target)<mind) { mind = Math.abs(v-target); res = v; } if (v < target) l++; else if (v > target) r--; else return v; } } return res; }