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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. const int maxn = 400 + 20;
  4. int n, m, s, t;
  5.  
  6. bool inq[maxn];
  7. int g[maxn][maxn], dis[maxn];
  8. vector<int> ans[maxn];
  9. void spfa() {
  10. 	queue<int> que;
  11. 	memset(dis, 0x3f, sizeof dis);
  12. 	que.push(s), dis[s] = 0, inq[s] = true;
  13. 	while(!que.empty()) {
  14. 		int u = que.front(); que.pop();
  15. 		inq[u] = false;
  16. 		for(int i = 1; i <= n; ++i) {
  17. 			if(g[u][i] != 0 && dis[i] > dis[u] + 1) {
  18. 				dis[i] = dis[u] + 1;
  19. 				if(!inq[i]) {
  20. 					que.push(i);
  21. 					inq[i] = true;
  22. 				}
  23. 			}
  24. 		}
  25. 	}
  26. }
  27.  
  28. int main() {
  29. 	scanf("%d%d%d%d", &n, &m, &s, &t);
  30. 	for(int i = 1; i <= m; ++i) {
  31. 		int u, v;
  32. 		scanf("%d%d", &u, &v);
  33. 		g[u][v] = g[v][u] = i;
  34. 	}
  35. 	spfa();
  36. 	for(int i = 1; i <= n; ++i) {
  37. 		for(int j = 1; j <= n; ++j) {
  38. 			if(g[i][j] && dis[j] == dis[i] + 1) {
  39. 				ans[dis[i]].push_back(g[i][j]);
  40. 				g[i][j] = g[j][i] = 0;
  41. 			}
  42. 		}
  43. 	}
  44. 	for(int i = 1; i <= n; ++i) {
  45. 		for(int j = 1; j <= n; ++j) {
  46. 			if(g[i][j]) {
  47. 				ans[dis[t]].push_back(g[i][j]);
  48. 				g[i][j] = g[j][i] = 0;
  49. 			}
  50. 		}
  51. 	}
  52. 	printf("%d\n", dis[t]);
  53. 	for(int i = 0; i < dis[t]; ++i) {
  54. 		printf("%d", (int)ans[i].size());
  55. 		for(int j = 0, sz = ans[i].size(); j < sz; ++j) {
  56. 			printf(" %d", ans[i][j]);
  57. 		}
  58. 		puts("");
  59. 	}
  60. 	return 0;
  61. }
  62.  
Success #stdin #stdout 0s 4176KB
comments (?)
stdin
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4 4 1 4 
1 2 
1 3 
2 4 
3 4
stdout
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2
2 1 2
2 3 4
https://ideone.com/fothPV
SGU 213. Strong Defence
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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