UVa 10305 Ordering Tasks (例题 6-15)
传送门: https://uva.onlinejudge.org/external/103/10305.pdf
拓扑排序(topological sort)简单题
自己代码的思路来自: ==> http://songlee24.github.io/2015/05/07/topological-sorting/
感谢n久前蔡大神扔给我这个链接2333333
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 const int MAXN = 111; 5 bool vis[MAXN]; 6 int G[MAXN][MAXN]; 7 int indegree[MAXN]; 8 int main(){ 9 int n, m; 10 while(cin >> n >> m){ 11 if(n == 0 && m == 0) break; 12 memset(vis, false, sizeof(vis)); 13 memset(G, 0, sizeof(G)); 14 memset(indegree, 0, sizeof(indegree)); 15 for(int i = 0; i < m; ++i){ 16 int a, b; 17 cin >> a >> b; 18 G[a][b] = 1; 19 indegree[b] += 1; 20 } 21 queue<int> q; 22 while(!q.empty()) q.pop(); 23 for(int i = 1; i <= n; ++i) 24 if(!indegree[i]) q.push(i); 25 int total = n; 26 while(!q.empty()){ 27 int cur = q.front(); 28 q.pop(); 29 cout << cur; 30 if(--total) cout << " "; 31 vis[cur] = true; 32 for(int i = 1; i <= n; ++i){ 33 if(G[cur][i]){ 34 --indegree[i]; 35 if(!indegree[i] && !vis[i]) 36 q.push(i); 37 } 38 } 39 } 40 cout << endl; 41 } 42 return 0; 43 }
入门经典的思路：
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 const int MAXN = 111; 5 int n, m, t; 6 int vis[MAXN]; 7 int topo[MAXN]; 8 int G[MAXN][MAXN]; 9 10 bool dfs(int cur){ 11 //vis数组存储三个状态{-1, 0, 1} 12 //-1 代表该点正在访问中(正在栈帧中) 13 // 0 代表该点没有被访问过 14 // 1 代表该点及所有有关系的点都被访问过了 15 vis[cur] = -1; 16 for(int i = 1; i <= n; ++i) 17 if(G[cur][i]){ 18 //若在访问中遇到符合要求且正在调用的点,证明图存在有向环,不存在拓扑排序 19 if(vis[i] < 0) return false; 20 else if(!vis[i] && !dfs(i)) return false; 21 } 22 vis[cur] = 1; 23 topo[--t] = cur; 24 return true; 25 } 26 bool toposort(){ 27 t = n; 28 memset(vis, 0, sizeof(vis)); 29 memset(topo, 0, sizeof(topo)); 30 for(int i = 1; i <= n; ++i) 31 if(!vis[i]) 32 if(!dfs(i)) 33 return false; 34 return true; 35 } 36 int main(){ 37 while(cin >> n >> m){ 38 if(n == 0 && m == 0) break; 39 memset(G, 0, sizeof(G)); 40 while(m--){ 41 int a, b; 42 cin >> a >> b; 43 G[a][b] = 1; 44 } 45 if(toposort()) 46 for(int i = 0; i < n; ++i) cout << topo[i] << " \n"[i == n-1]; 47 } 48 return 0; 49 }
