3Sum Closest
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).
先确定第一个数字，然后用双指针遍历，不断更新最接近的值。
复杂度O(n2)
class Solution { public: int threeSumClosest(vector<int> &num, int target) { int gap = INT_MAX; int sum = 0; sort(num.begin(), num.end()); for(int i = 0; i < num.size()-2; i ++) { int j = i+1; int k = num.size()-1; while(j < k) { int tmp = num[i]+num[j]+num[k]; if(abs(tmp-target) < gap) { gap = abs(tmp-target); sum = tmp; } if(tmp == target) return target; else if(tmp < target) j ++; else k --; } } return sum; } };
原文：http://www.cnblogs.com/ganganloveu/p/4176327.html