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.

思路：同３Ｓｕｍ题目，使用三个指针。

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).

#include <stdlib.h>
#include <algorithm>
class Solution {
public:
int threeSumClosest(vector<int>& nums, int target) {
if(nums.size() < 3)
return 0;
int result = nums[0] + nums[1] + nums[2];
sort(nums.begin(), nums.end());
for(int i = 0 ; i <= nums.size()-3; i++)
{
int j = i + 1;
int k = nums.size() - 1;
while(j < k){
int sum = nums[i] + nums[j] + nums[k];
if(sum > target){
k--;
}
else if(sum < target){
j++;
}else
return target;
//update the sum.
if(abs(sum - target) < abs(result - target)){
result = sum;
}
}
}
return result;
}
};

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