LeetCode 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).
此题与上体3sum类似，只不过这里需要用sum来和target比较决定指针+1,还是-1,同样这里需要先对元素排序，代码如下：

void insertsort2(vector<int> &num)
{
    int nSize = num.size();
    int j = 0;

    for(int i = 1; i< nSize; ++i)
    {
        int temp = num[i];
        for( j = i; j>0 && temp < num[j-1] ; --j)
        {
            num[j] = num[j-1];
        }
        num[j] = temp;
    }
}
int threeSumClosest(vector<int>& nums, int target)
{
    int nSize = nums.size();
    int sum = 0;
    int dist = INT_MAX;
    int nPrevDist = INT_MAX;
    insertsort2(nums);

    if(nSize < 3)
    {
        return -1;
    }
    for(int i = 0; i!=nSize; ++i)
    {
        int p = i+1;
        int q = nSize - 1;
        while(p < q)
        {
            sum = nums[i] + nums[p] + nums[q];
            int temp = abs(sum - target);
            if(temp < nPrevDist)
            {
                nPrevDist = temp;
                dist = sum;
            }
            if(sum > target)
            {
                --q;
            }
            else
            {
                ++p;
            }
        }
    }
    return dist;

}

需要多思考如何借鉴运用已有的算法。