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

 #include <bits/stdc++.h>
 using namespace std;

 const int MAXN = ;
 bool vis[MAXN];
 int G[MAXN][MAXN];
 int indegree[MAXN];
 int main(){
     int n, m;
     while(cin >> n >> m){
         if(n ==  && m == ) break;
         memset(vis, false, sizeof(vis));
         memset(G, , sizeof(G));
         memset(indegree, , sizeof(indegree));
         for(int i = ; i < m; ++i){
             int a, b;
             cin >> a >> b;
             G[a][b] = ;
             indegree[b] += ;
         }
         queue<int> q;
         while(!q.empty()) q.pop();
         for(int i = ; i <= n; ++i)
             if(!indegree[i]) q.push(i);
         int total = n;
         while(!q.empty()){
             int cur = q.front();
             q.pop();
             cout << cur;
             if(--total) cout << " ";
             vis[cur] = true;
             for(int i = ; i <= n; ++i){
                 if(G[cur][i]){
                     --indegree[i];
                     if(!indegree[i] && !vis[i])
                         q.push(i);
                 }
             }
         }
         cout << endl;
     }
     return ;
 }

入门经典的思路：

 #include <bits/stdc++.h>
 using namespace std;

 const int MAXN = ;
 int n, m, t;
 int vis[MAXN];
 int topo[MAXN];
 int G[MAXN][MAXN];

 bool dfs(int cur){
     //vis数组存储三个状态{-1, 0, 1}
     //-1 代表该点正在访问中(正在栈帧中)
     // 0 代表该点没有被访问过
     // 1 代表该点及所有有关系的点都被访问过了
     vis[cur] = -;
     for(int i = ; i <= n; ++i)
         if(G[cur][i]){
             //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
             if(vis[i] < ) return false;
             else if(!vis[i] && !dfs(i)) return false;
         }
     vis[cur] = ;
     topo[--t] = cur;
     return true;
 }
 bool toposort(){
     t = n;
     memset(vis, , sizeof(vis));
     memset(topo, , sizeof(topo));
     for(int i = ; i <= n; ++i)
         if(!vis[i])
             if(!dfs(i))
                 return false;
     return true;
 }
 int main(){
     while(cin >> n >> m){
         if(n ==  && m == ) break;
         memset(G, , sizeof(G));
         while(m--){
             int a, b;
             cin >> a >> b;
             G[a][b] = ;
         }
         if(toposort())
             for(int i = ; i < n; ++i) cout << topo[i] << " \n"[i == n-];
     }
     return ;
 }