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.
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).
class Solution { public: int threeSumClosest(vector<int> &num, int target) { if (num.size() < 3) return -1; sort(num.begin(), num.end()); int closest = num[0] + num[1] + num[2]; for (int i=0; i<num.size(); i++) { int p = i+1, q = num.size()-1; while (p < q) { const int diff = num[i] + num[p] + num[q] - target; if (abs(diff) < abs(closest-target)) closest = diff + target; if (!diff) return closest; else if (diff < 0) ++p; else --q; } } return closest; } };