【紫书】Ordering Tasks UVA - 10305 拓扑排序：dfs到底再输出。

题意：给你一些任务1~n，给你m个数对（u,v)代表做完u才能做v 让你给出一个做完这些任务的合理顺序。

题解：拓扑排序版题 dfs到底再压入栈。

#define _CRT_SECURE_NO_WARNINGS
#include "stdio.h"
#include<stdio.h>
#include<algorithm>
#include<string>
#include<vector>
#include<list>
#include<set>
#include<iostream>
#include<string.h>
#include<queue>
#include<string>
#include<sstream>
using namespace std;
const int maxn =  + ;
int G[maxn][maxn];
int c[maxn];
list<int>topo;
int n, m;
bool dfs(int u) {
    c[u] = -;
    for (int v = ; v <= n; v++)if(G[u][v]) {
        if (c[v] == -)return false;//正在dfs栈中
        else if (!c[v] && !dfs(v))return false;//若未dfs，就dfs一遍.
    }
    c[u] = ; topo.push_front(u);
    return true;
}
bool toposort() {
    memset(c, , sizeof(c));
    for (int u = ; u <= n; u++)if(c[u]==) {
        if (!dfs(u))return false;
    }
    return true;
}
int main() {

    while (cin >> n >> m)
    {
        if (n == m&&n == )break;
        memset(G, , sizeof(G));
        topo.clear();
        for (int i = ; i < m; i++) {
            int a, b;
            cin >> a >> b;
            G[a][b] = ;
        }
        if (toposort()) {
            cout << topo.front();
            topo.pop_front();
            for (auto t : topo) cout << ' '<< t ;
            cout << endl;
        }
    }

    system("pause");
    return ;
}

附：不判环的ac代码（便于理解）

#include "stdio.h"
#include<stdio.h>
#include<algorithm>
#include<string>
#include<vector>
#include<list>
#include<set>
#include<iostream>
#include<string.h>
#include<queue>
#include<string>
#include<sstream>
#include<stack>
using namespace std;
const int maxn =  + ;
vector<int> G[maxn];
int c[maxn];
stack<int>topo;
int n, m;
void dfs(int u) {
    c[u] = ;
    for (int j = ; j <G[u].size(); j++)
    {
        int v = G[u][j];
        if (!c[v])dfs(v);
    }
    c[u] = ; topo.push(u);

}
void toposort() {
    memset(c, , sizeof(c));
    for (int u = ; u <= n; u++)if(c[u]==) {dfs(u);}
}
int main() {

    while (cin >> n >> m)
    {
        if (n == m&&n == )break;
        for (int i = ; i <= n; i++)G[i].clear();
        while (!topo.empty()) topo.pop();
        for (int i = ; i < m; i++) {
            int a, b;
            cin >> a >> b;
            G[a].push_back(b);
        }
        toposort();
        cout << topo.top(); topo.pop();
        while (!topo.empty()) {
            cout << ' ' << topo.top(); topo.pop();
        }
        cout << endl;
    }

    system("pause");
    return ;
}