[leetcode] 16. 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).

这道题是找出数组中三个数相加最接近给定值的相加和，题目难度为Medium。

这道题基本和第15题一样，解题思路请查看第15题（传送门）的详解。不同的地方是需要记录下当前最接近给定值的相加和，每次进行判断取最接近的替换记录值。具体代码：

class Solution {
public:
int threeSumClosest(vector<int> &num, int target) {
int rst = 0;

if(num.size() < 3) return 0;

sort(num.begin(), num.end());

rst = num[0] + num[1] + num[2];
for(int i=0; i<num.size()-2; i++) {
if(i > 0 && num[i] == num[i-1]) continue;

for(int j=i+1, k=num.size()-1; j<k;) {
int sum = num[i] + num[j] + num[k];
if(abs(sum-target) < abs(rst-target)) rst = sum;
if(sum < target) {
do {j++;} while(num[j] == num[j-1] && j < k);
}
else if(sum > target) {
do {k--;} while(num[k] == num[k+1] && j < k);
}
else {
return target;
}
}
}

return rst;
}
};