对于leetcode一道算法题的问题

leetcode的第16道题，关于数组的一道算法题，在下的代码不能通过测试集，但是在下实在不知错误出在哪里，特来此处，请帮帮在下。
问题：
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).

在下的代码：

 class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int size = nums.size();  //取数组大小 方便判断
        if (size<3)
            return 0;
        std::sort(nums.begin(), nums.end());  //排序 方便后续操作
        int gap = INT_MAX;  //存储与target相差的值
        for(int i=0;i<size-2;++i){  //因为是三数之和 所以在循环到size-2
            int front = i+1;  //第二个加数
            int back = size-1;  //第三个家数
            while(front<back){  //在for循环内进行第二次循环 以此判断在第一个加数确定的情况下的各种情况
            int sum = nums[i]+nums[front]+nums[back];  //取三数之和
            if(abs(gap)>abs(sum-target))  //判断相差值的大小 如果相差值变大 则gap不变 若相差值变小 则gap更新
                gap=sum-target;
            if (gap == 0)
                return sum;  //相等 返回和
            else if(gap>0)  
                 back--; //较大  让第三个加数变小
            else
                front++;  //较小 让第二个加数变大
            }
            while(i<size-2&&nums[i+1]==nums[i])  //该循环用于跳过不必要的元素
                i++;
        }
        return (gap+target);
    }
};

你的代码会漏算一些case,按照轮询写的话，你试试

 int threeSumClosest(vector<int>& nums, int target)
{
    int size = nums.size();  //取数组大小 方便判断
    if (size < 3)
        return 0;
    std::sort(nums.begin(), nums.end());  //排序 方便后续操作
    int gap = INT_MAX;  //存储与target相差的值
    int iSum = 0;
    int iPreSum = iSum;
    bool bSetPreSum = false;
    bool bFind = false;
    int index, index2, index3;
    for (int i = 0; i < size - 2; i++)
    {
        if (bFind)
        {
            break;
        }
        for (int i2 = i + 1; i2 < size - 1; i2++)
        {
            if (bFind)
            {
                break;
            }

            for (int i3 = i2 + 1; i3 < size; i3++)
            {
                iSum = nums[i] + nums[i2] + nums[i3];
                if (!bSetPreSum)
                {
                    iPreSum = iSum;
                    index = i;
                    index2 = i2;
                    index3 = i3;
                    bSetPreSum = true;
                }

                if (iSum == target)
                {
                    bFind = true;
                    iPreSum = iSum;
                    index = i;
                    index2 = i2;
                    index3 = i3;
                    break;
                }
                else if (abs(iSum - target) < abs(iPreSum - target))
                {
                    iPreSum = iSum;
                    index = i;
                    index2 = i2;
                    index3 = i3;
                }
            }
        }
    }

    bFind = true;
    printf("closest sum = %d + %d + %d = %d\n", nums[index], nums[index2], nums[index3], (iPreSum));
    return iSum;
}