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  1. #include <bits/stdc++.h> 
  2.  
  3. using namespace std;  
  4.  
  5. typedef long long ll;  
  6. typedef pair<int, int> ii;  
  7.  
  8. const int INF = 1e9;  
  9. const ll LINF = 1e18;  
  10.  
  11. const int N = 2e3 + 5; 
  12.  
  13. int n, m;  
  14. vector<int> adj[N]; 
  15.  
  16. int tin[N], low[N], timer;  
  17. int id[N];
  18. vector<int> st;  
  19. bool in_stack[N]; 
  20.  
  21. void dfs(int u) {
  22. 	tin[u] = low[u] = ++timer;   
  23. 	st.push_back(u);   
  24. 	in_stack[u] = true;  
  25.  
  26. 	for (int v : adj[u]) {
  27. 		if (!tin[v]) {
  28. 			dfs(v);  
  29. 		}
  30. 		if (in_stack[v]) {
  31. 			low[u] = min(low[u], low[v]); 
  32. 		}
  33. 	}
  34.  
  35. 	if (low[u] == tin[u]) {
  36. 		while (true) {
  37. 			int v = st.back(); st.pop_back();  
  38. 			in_stack[v] = false; 
  39. 			id[v] = u;
  40. 			if (v == u) break; 
  41. 		}
  42. 	}
  43. }
  44.  
  45. int indeg[N];
  46. int outdeg[N];  
  47.  
  48. int main() {
  49. 	ios::sync_with_stdio(false); 
  50. 	cin.tie(nullptr); 	
  51. 	cin >> n >> m; 
  52.  
  53. 	for (int i = 0; i < m; i++) {
  54. 		int u, v; 
  55. 		cin >> u >> v; 
  56. 		adj[u].push_back(v); 
  57. 	}
  58.  
  59. 	timer = 0; 
  60. 	for (int u = 1; u <= n; u++) {
  61. 		if (!tin[u]) dfs(u); 
  62. 	}
  63.  
  64. 	for (int u = 1; u <= n; u++) {
  65. 		for (int v : adj[u]) {
  66. 			if (id[u] == id[v]) continue;   
  67. 			outdeg[id[u]]++; 
  68. 			indeg[id[v]]++; 
  69. 		}
  70. 	}
  71.  
  72. 	int cnt_s = 0, cnt_t = 0;   
  73. 	int s = -1, t = -1; 
  74.  
  75. 	for (int u = 1; u <= n; u++) {
  76. 		if (u != id[u]) continue;      
  77. 		if (indeg[u] == 0) {
  78. 			cnt_s++;    
  79. 			s = u;  
  80. 		}
  81. 		if (outdeg[u] == 0) {
  82. 			cnt_t++;  
  83. 			t = u; 
  84. 		}
  85. 	}
  86.  
  87. 	if (cnt_s == 1 && cnt_t == 1) {
  88. 		cout << "YES" << '\n'; 
  89. 		cout << t << ' ' << s << '\n'; 
  90. 	} 
  91. 	else {
  92. 		cout << "NO" << '\n'; 
  93. 	}
  94. }
  95.  
Success #stdin #stdout 0.01s 5284KB
comments (?)
stdin 
3 2
1 2
2 3
stdout 
YES
3 1
https://ideone.com/c4gmYn
language:
C++14 (gcc 8.3)
created:
259 days ago
visibility:
secret

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