[LeetCode] 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).

分析：

同3sum 一样，但不用去重，

class Solution {
public:
    int threeSumClosest(vector<int> &num, int target) {
        
        int n =  num.size();
        
        sort(num.begin(), num.end());
        
        
        int a, b,c;
        int min_gap = INT_MAX;
        int ret = 0;
                
        for(int a = 0; a < n-2; a++)
        {
            b = a +1;
            c = n-1;
            
            while(b < c)
            {
                int sum = num[a] + num[b] + num[c];
                int gap = abs(sum - target) ;
                if(gap < min_gap)
                {
                    min_gap = gap;
                    ret = sum;
                }
                
               if(sum < target)
                    b++;
                else if(sum > target)
                    c--;
                else
                    return target;
            }
        }
        
        return ret;
        
    }
};