[LeetCode16]3Sum Closest

题目：

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).

分类：Array TwoPointers

代码：

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) 
    {
        int n = nums.size();
        int sum = 0;
        if(n <= 3)
        {
            return accumulate(nums.begin(),nums.end(),0);
        }
        sort(nums.begin(),nums.end());
        
        int temp = nums[0] + nums[1] + nums[2];
        for(int i = 0; i < n - 2; ++i)
        {
            int j = i + 1;
            int k = n - 1;
            while(j < k)
            {
                sum = nums[i] + nums[j] + nums[k];
                if(abs(target - sum) < abs(target - temp))
                {
                    temp = sum;
                    if(temp == target)
                        return  temp;
                }
                if(sum > target)
                {
                    k--;
                }
                else
                {
                    j++;
                }
            }
        }
        return  temp;
    }
};