简单易懂，新手可看

#include <bits/stdc++.h>
using namespace std;
bool cmp(int a,int b){
    return a > b;
}
int main(){
    int n,a[1005],cnt1 = 0,cnt2 = 0,t1 = 2,t2 = 0;
    cin >> n;
    for(int i = 1;i <= n;i++) cin >> a[i];
    sort(a+1,a+n+1,cmp);
    for(int i = 1;i <= n;i++){
        if(i == 1) cnt1 += a[i];
        else{
            t2++;
            if(t1 == 1) cnt1 += a[i];
            else cnt2 += a[i];
            if(t2 == 2){
                t2 = 0;
                if(t1 == 1) t1 = 2;
                else t1 = 1;
            }
        }  
    }
    if(cnt1 > cnt2) cout << cnt1 - cnt2;
    else cout << cnt2 - cnt1;
}