3 Sum Closest详解编程语言

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).

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