Rails - URI - UVA 514

#include <bits/stdc++.h>

#define forn(l, r) for(int i = l; i < (r); ++i)
#define forj(l, r) for(int j = l; j < (r); ++j)
#define TAM 1000100
#define SYNC ios::sync_with_stdio(0);
#define $ << ' ' <<
#define F first
#define S second
#define endl '\n'


using namespace std;

using ll = long long int;
using ii = pair<int, int>;
using vii = vector<ii>;
using vi = vector<int>;
using graph = vector<vi>;
const int INF = 0x3f3f3f3f;
const int MAXN = 112345;
const ll mod = 1000000007;


int main() {
    //SYNC
    vector<string> ans;
    stack<int> ptA, stt;
    queue<int> ptB;
    int n, vag;
    while (cin >> n && n) {
        while (cin >> vag && vag) {
            while(!ptA.empty()) ptA.pop();
            while(!ptB.empty()) ptB.pop();
            while(!stt.empty()) stt.pop();
            for (int i = n; i > 0; --i) {
                ptA.push(i);
            }
            ptB.push(vag);
            for (int i = 1; i < n; ++i) {
                int j;
                cin >> j;
                ptB.push(j);
            }
            while (!ptA.empty()) {
                //cout << "x\n";
                stt.push(ptA.top());
                ptA.pop();
                //cout << stt.top() << ' ' << ptB.front() << endl;
                while (!stt.empty() && stt.top() == ptB.front()) {
                    stt.pop();
                    ptB.pop();
                }
            }

            if (stt.empty()) ans.push_back("Yes");
            else ans.push_back("No");
        }
        if (!vag) {
            ans.push_back("");
        }
    }
    for (auto x : ans) {
        cout << x << endl;
    }
    return 0;
}