Contents

1. 1. 题意：
2. 2. 分析：

/*

• 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).

• */

题意：

在给定数列中找出三个数，使和最接近 target。

分析：

先排序，再左右夹逼。

class Solution {  
public:  
    int threeSumClosest(vector<int> &num, int target) {  
        int ret = num[0] + num[1] + num[2];  
        int len = num.size();  
  
        sort(num.begin(), num.end());  
  
        for (int i = 0; i <= len - 3; i++) {  
            // first number : num[i]  
            int j = i + 1;  // second number  
            int k = len - 1;    // third number  
            while (j < k) {  
                int sum = num[i] + num[j] + num[k];  
                if (abs(sum - target) < abs(ret - target))  
                    ret = sum;  
                if (sum < target) {  
                    ++j;  
                } else if (sum > target) {  
                    --k;  
                } else {  
                    ++j;  
                    --k;  
                }  
            }  
        }  
        return ret;  
    }  
};