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- // баобаб
- #include <iostream>
- #include <cmath>
- #include <vector>
- #include <queue>
- #include <set>
- #include <iterator>
- using namespace std;
- vector <int> mark(10000);
- vector<set<int>> gr(10000);
- int mas[105][105];
- int ans = 0;
- int kol_reb = 0; // количество ребер
- void in_set(int n)
- {
- for (int i = 0; i < n; i++)
- {
- for (int j = 0; j < n; j++)
- {
- if (mas[i][j] == 1)
- {
- gr[i].insert(j);
- kol_reb++;
- }
- }
- }
- kol_reb /= 2;
- return;
- }
- void DFS_cycle(int v, int pr) // проверка, есть ли цикл
- {
- mark[v] = 1;
- for (int i : gr[v])
- {
- if (mark[i] == 0)
- {
- DFS_cycle(i, v);
- }
- else if (i != pr)
- {
- ans++;
- }
- }
- return;
- }
- signed main()
- {
- int n;
- cin >> n;
- for (int i = 0; i < n; i++)
- {
- for (int j = 0; j < n; j++)
- {
- cin >> mas[i][j];
- }
- }
- in_set(n);
- if (kol_reb != n - 1)
- {
- cout << "NO";
- sp;
- return 0;
- }
- for (int i = 1; i <= n; i++)
- {
- for (int i = 0; i <= n; i++)
- {
- mark[i] = 0;
- }
- DFS_cycle(i, -1);
- }
- if (ans != 0)
- {
- cout << "NO";
- }
- else
- {
- cout << "YES";
- }
- return 0;
- }
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