Is it a Tree?

    1#include <bits/stdc++.h>
    2using namespace std;
    3int main(){
    4    int n = 4, m = 4, cnt = 0;
    5    vector<vector<int>> adj(n);
    6    for(int i = 0; i < n; i++){
    7        for(int j = 0; j < m; j++){
    8            int x; cin >> x;
    9            if(x){
    10                adj[i].push_back(j);
    11                adj[j].push_back(i);
    12                if(i < j) cnt++;
    13            }
    14        }
    15    }
    16    if(cnt != 3){
    17        cout << "No" << '\n';
    18         exit(0);
    19    }
    20    vector<bool> vis(n);
    21    queue<int> q;
    22    q.push(0); vis[0] = true;
    23    while(!q.empty()){
    24        int u = q.front(); q.pop();
    25        for(int v : adj[u]){
    26            if(!vis[v]){
    27                vis[v] = true;
    28                q.push(v);
    29            }
    30        }
    31    }
    32    bool good = 1;
    33    for(int i = 0; i < n; i++){
    34        if(!vis[i]) good = 0;
    35    }
    36    if(good) cout << "Yes" << '\n';
    37    else cout << "No" << '\n';
    38    return 0;
    39}