A Noisy Class

    1#include <bits/stdc++.h>
    2using namespace std;
    3int main(){
    4    ios::sync_with_stdio(0); cin.tie(0);
    5    int n, m; cin >> n >> m;
    6    vector<vector<int>> adj(n);
    7    vector<int> indegree(n);
    8    for(int i = 0; i < m; i++){
    9        int a, b; cin >> a >> b;
    10        a--; b--;
    11        adj[a].push_back(b);
    12        indegree[b]++;
    13    }
    14    queue<int> q;
    15    for(int i = 0; i < indegree.size(); i++){
    16        if(!indegree[i]) q.push(i);
    17    }
    18    int cnt = 0;
    19    while(!q.empty()){
    20        cnt++;
    21        int cur = q.front(); q.pop();
    22        for(int nxt : adj[cur]){
    23            if(!--indegree[nxt]) q.push(nxt);
    24        }
    25    } 
    26    if(cnt == n){
    27        cout << "Y" << '\n';
    28    } else {
    29        cout << "N" << '\n';
    30    }
    31}