一道ACM试题，求大神解答，如果有代码就更好了

Question

Answer 1

#include<iostream>
#include<stack>
using namespace std;
int main(){
    int n;
    while(cin>>n,n){
        stack<int> p;
        for (int i = 0; i < n;++i) {
            int num;
            cin >> num;
            if(p.empty()){
                p.push(num);
            }
            else if(p.top()!=num){
                p.pop();
            }
            else if(p.top()==num){
                p.push(num);
            }
        }
        cout << p.top() << endl;
    }
}