16. 3Sum Closest

先排序，然后左右夹逼，
每次当sum-target < diff 用diff记录下最小距离

static int intcmp(const void *a, const void *b)
{
    return(*(int *)a - *(int *)b);
}



int threeSumClosest(int* nums, int numsSize, int target) {
    
    qsort(nums, numsSize, sizeof(nums[0]), intcmp);

    int res=0, sum=0, diff=2147483647, start, end;
    
    for(int i=0; i<=numsSize-3;i++)
    {
        if(i>0 && nums[i]==nums[i-1])
            continue;
        
        start = i+1;
        end = numsSize-1;
        
        while(start<end)
        {
            sum = nums[i] + nums[start] + nums[end];
            if(sum<target){
                if(target-sum < diff)
                {
                    diff = target-sum;
                    res = sum;
                }    
                start++;
            }
            else if(sum>target){
                if(sum-target < diff)
                {
                    diff = sum-target;
                    res = sum;
                }    
                end--; 
            }
            else
                return sum;
        }    
        
    }    
    
    return res;
}