給定一個圖,並給定邊,a b c(c==1||c==2) 表示ab之間有c條邊 求把儘可能多的有向邊定向變成強聯通圖。

先把圖當做無向圖,加邊時記錄是否有邊,dfs的時候不要把本沒有的邊用到!因為這個錯了好多次。。。。然後就簡單了,記錄橋就可以了。

  1. /**************************************************
  2. Problem: 1438 User: G_lory
  3. Memory: 5312K Time: 657MS
  4. Language: C++ Result: Accepted
  5. **************************************************/
  6. #include <cstdio>
  7. #include <cstring>
  8. #include <iostream>
  9. #define pk printf("KKK!\n");
  10.  
  11. using namespace std;
  12.  
  13. const int N = 2005;
  14. const int M = N * N;
  15.  
  16. struct Edge {
  17. int from, to, next;
  18. int flag; // 1代表單向邊 0代表沒邊 2代表雙向邊
  19. int cut;
  20. } edge[M];
  21. int cnt_edge;
  22. int head[N];
  23. void add_edge(int u, int v, int c)
  24. {
  25. edge[cnt_edge].from = u;
  26. edge[cnt_edge].to = v;
  27. edge[cnt_edge].next = head[u];
  28. edge[cnt_edge].flag = c;
  29. edge[cnt_edge].cut = 0;
  30. head[u] = cnt_edge++;
  31. }
  32.  
  33. int dfn[N]; int idx;
  34. int low[N];
  35.  
  36. int n, m;
  37.  
  38. void tarjan(int u, int pre)
  39. {
  40. dfn[u] = low[u] = ++idx;
  41. for (int i = head[u]; i != -1; i = edge[i].next)
  42. {
  43. int v = edge[i].to;
  44. if (edge[i].flag == 0) continue;
  45. if (edge[i].cut == 0)
  46. {
  47. edge[i].cut = 1;
  48. edge[i ^ 1].cut = -1;
  49. }
  50. if (v == pre) continue;
  51.  
  52. if (!dfn[v])
  53. {
  54. tarjan(v, u);
  55. low[u] = min(low[u], low[v]);
  56. if (dfn[u] < low[v])
  57. {
  58. edge[i].cut = 2;
  59. edge[i ^ 1].cut = -1;
  60. }
  61. }
  62. else low[u] = min(low[u], dfn[v]);
  63. }
  64. }
  65.  
  66. void init()
  67. {
  68. idx = cnt_edge = 0;
  69. memset(dfn, 0, sizeof dfn);
  70. memset(head, -1, sizeof head);
  71. }
  72.  
  73. void solve()
  74. {
  75. for (int i = 0; i < cnt_edge; ++i)
  76. if (edge[i].flag == 2 && (edge[i].cut == 1 || edge[i].cut == 2))
  77. printf("%d %d %d\n", edge[i].from, edge[i].to, edge[i].cut);
  78. }
  79.  
  80. int main()
  81. {
  82. //freopen("in.txt", "r", stdin);
  83. while (~scanf("%d%d", &n, &m))
  84. {
  85. if (n == 0 && m == 0) break;
  86. int u, v, c;
  87. init();
  88. for (int i = 0; i < m; ++i)
  89. {
  90. scanf("%d%d%d", &u, &v, &c);
  91. add_edge(u, v, c);
  92. if (c == 1) c = 0;
  93. add_edge(v, u, c);
  94. }
  95. tarjan(1, -1);
  96. solve();
  97. }
  98. return 0;
  99. }