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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. int n,m;
  4. vector<vector<int>> inp;
  5. vector<int> low, num, dp;
  6. vector<bool> vis;
  7. int times = 0;
  8. int ans_cur = 0;
  9. void dfs(int u, int par)
  10. {
  11. 	low[u] = num[u] = ++times;
  12. 	int child = 1;
  13. 	int mx = 0;
  14. 	for(int x: inp[u])
  15. 	{
  16. 		if(x == par) continue;
  17.  
  18. 		if(num[x] == 0)
  19. 		{
  20. 			dfs(x, u);
  21. 			child++;
  22. 			low[u] = min(low[u], low[x]);
  23.  
  24. 			if(low[x] == num[x])
  25. 			{
  26. 				mx = max(mx, dp[x] +1);
  27. 			}
  28.  
  29. 		}
  30. 		else if(num[x] < num[u]) low[u] = min(low[u], num[x]);
  31. 	}
  32. 	dp[u] = mx;
  33. }
  34.  
  35.  
  36. void dfs_vis(int u, int par)
  37. {
  38. 	int child = 0;
  39. 	vis[u] = true;
  40. 	int mx = 0;
  41. 	int mx2 = 0;
  42. 	for(int x: inp[u])
  43. 	{
  44. 		if(vis[x]) continue;
  45. 		dfs_vis(x, u);
  46. 		child++;
  47. 		bool tmp = false;
  48. 		if( low[x] == num[x]) {  tmp = true; }
  49. 		if(mx < dp[x] + tmp)
  50. 		{
  51. 			mx2 =mx;
  52. 			mx = dp[x]  + tmp;
  53.  
  54. 		}
  55. 		else if( mx2  < dp[x] + tmp && mx >= dp[x] + tmp) 
  56. 		{
  57. 			mx2 = dp[x] + tmp;
  58. 		}
  59. 	}
  60.  
  61. 	 ans_cur = max(ans_cur,  mx + mx2);
  62. }
  63. int main()
  64. {
  65. 	ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
  66. 	cin >> n >>m;
  67. 	inp.resize(n+1);
  68. 	low.resize(n+1);
  69. 	num.resize(n+1);
  70. 	dp.resize(n+1);
  71. 	for(int  i =1; i<=m; i++)
  72. 	{
  73. 		int a,b; cin >> a >> b;
  74. 		inp[a].push_back(b);
  75. 		inp[b].push_back(a);
  76. 	}
  77.  
  78. 	for(int i =1;i<=n; i++) if(num[i] == 0) dfs(i, i);
  79. 	vis.resize(n+1);
  80. 	int ans = 0;
  81. 	for(int i =1; i<=n; i++)
  82. 	{
  83. 		if(vis[i] == false)
  84. 		{
  85. 			dfs_vis(i, i);
  86. 			ans = max(ans, ans_cur);
  87. 			ans_cur = 0;
  88. 		}
  89. 	}
  90. 	cout << ans;
  91. 	return 0;
  92. }
Success #stdin #stdout 0s 5320KB
comments (?)
stdin
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7 10
4 5
3 7
6 2
3 4
1 6
7 4
2 7
3 2
2 5
5 6
stdout
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1
https://ideone.com/CnK2RK
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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