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).

解题思路：（1）先对数组进行希尔排序
（2）第一个数从1到n依次枚举
（3）设置两个指针分别指向第二个数和第三个数，第一个指针从前往后，第二个指针从后往前

int threeSumClosest(int* nums, int numsSize, int target) {

//希尔排序
for (int Incre = numsSize/2; Incre > 0; Incre /= 2)
{
    for (int i = Incre; i < numsSize; i++)
    {
        int temp = nums[i];
        int j;
        for (j = i; j >= Incre; j -= Incre)
        {
            if (temp < nums[j-Incre])
                nums[j] = nums[j-Incre];
            else
                break;
        }
        nums[j] = temp;
    }
}

int sum;
int minsum = nums[0]+nums[1]+nums[2];

for (int i = 0; i < numsSize; i++)
{
    int j = i+1;
    int k = numsSize-1;

    while (j < k)
    {
        sum = nums[i]+nums[j]+nums[k];

        if (sum == target)
            return target;
        else if (sum > target)
            k--;
        else
            j++;

        if (abs(sum-target) < abs(minsum-target))
        {
            minsum = sum;
        }
    }
}

return minsum;

}