算法1

排个序，每隔两个相邻的减一下求和就好了，感觉算是简单题

时间复杂度 $O(nlogn)$

C++ 代码

#include<iostream>
#include<algorithm>
using namespace std;
const int N = 1e5 + 7;
int a[N];
int main()
{
    int n;
    cin >> n;
    for (int i = 0; i < n;i++)
        cin >> a[i];
    sort(a, a + n);
    int res = 0;
    for (int i = 1; i < n;i+=2)
        res += a[i] - a[i - 1];
    cout << res << endl;
    return 0;
}