【16】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).

与3 sum相似，只不过这里不是和0比，是和target比

int threeSumClosest(vector<int>& nums, int target) {
    sort(nums.begin(),nums.end());
    int n=nums.size();
    int ming,res;
    for(int m=1;m<n-1;m++){
        if(m>1 && nums[m]==nums[m-1] && nums[m-1]==nums[m-2])continue;
        int l=0,r=n-1;
        if(nums[m]==nums[m-1])l=m-1;
        while(l<m && r>m){
            int sum=nums[m]+nums[l]+nums[r];
            int gap=abs(sum-target);
            if(gap<ming){ming=gap;res=sum;}
            if(sum==target){
                return target;
                while(l+1<m && r-1>m && nums[l+1]==nums[l])l++;
                while(l+1<m && r-1>m && nums[r-1]==nums[r])r--;
                l++;
                r--;
            }
            else if(sum>target){
                while(l+1<m && r-1>m && nums[r-1]==nums[r])r--;
                r--;
            }
            else{
                while(l+1<m&& r-1>m && nums[l+1]==nums[l])l++;
                l++;
            }
        }
    }
    return res;
}