rt.比赛结束喽

# include <bits/stdc++.h>

using namespace std;

int n, num;

int main() {
    
    cin >> n;
    vector<int> p(n + 1); 
    for (int i = 1; i <= n; i++) {
        cin >> num;
        p[num] = i; 
    }
    bool is = true;
    vector<bool> s(n + 1, false); 
    for (int i = 1; i <= n; i++) {
        if (p[i] == 0 || s[p[i]]) {
            is = false;
            break;
        }
        s[p[i]] = true;
    }
    if (is) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }

    return 0;
}