求無序數組中三個元素相加與目標數最接近的三元素之和

/************************************************************************************************
**description:給定一個無序數組和一個目標數，要求返回數組中三個元素相加與目標數最接近的三元素之和
**            如：Input: a={-1 2 1 -4},target=1    Output: 2 (-1 + 2 + 1 = 2)
*************************************************************************************************/

//先排序，然後對有序數組遍歷，內層夾逼。
//時間複雜度O(n^2)，空間複雜度O(1)

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int threeSumClosest(vector<int> &arr, int target)
{
    int result = 0;
    int minDiff = 100;
    if (arr.size() < 3)
        return result;
    sort(arr.begin(), arr.end());
    for (int i = 0; i < arr.size() - 2; i++)
    {
        if (i > 0 && arr[i] == arr[i - 1])
            continue;
        int m = i + 1;
        int n = arr.size() - 1;
        while (m < n)
        {
            int diff = abs(target - arr[i] - arr[m] - arr[n]);
            if (diff < minDiff)
            {
                result = arr[i] + arr[m] + arr[n];
                minDiff = diff;
            }
            if (arr[i] + arr[m] + arr[n] < target)
                m++;
            else
                n--;
        }
    }
    return result;
}