bool dfs(int u) { vis[u] = -1; REP(i, 0, g[u].size()) { int v = g[u][i]; if(vis[v] == -1) return false; else if(!vis[v]) dfs(v); } vis[u] = 1; ans[--t] = u; //注意这里倒序加入 return true; } bool toposort() //可以用来判断有向图是否有环return false 则有环 { t = n; memset(vis, 0, sizeof(vis)); REP(i, 0, n) if(!vis[i] && !dfs(i)) return false; return true; }
裸题:UVa 10305
#include<cstdio> #include<vector> #include<cstring> #define REP(i, a, b) for(int i = (a); i < (b); i++) using namespace std; const int MAXN = 1123; vector<int> g[MAXN]; int vis[MAXN], ans[MAXN], n, m, t; bool dfs(int u) { vis[u] = -1; REP(i, 0, g[u].size()) { int v = g[u][i]; if(vis[v] == -1) return false; else if(!vis[v]) dfs(v); } vis[u] = 1; ans[--t] = u; return true; } bool toposort() { t = n; memset(vis, 0, sizeof(vis)); REP(i, 0, n) if(!vis[i] && !dfs(i)) return false; return true; } int main() { while(~scanf("%d%d", &n, &m) && n) { REP(i, 0, n) g[i].clear(); while(m--) { int u, v; scanf("%d%d", &u, &v); u--; v--; g[u].push_back(v); } if(toposort()) { REP(i, 0, n - 1) printf("%d ", ans[i] + 1); printf("%d\n", ans[n - 1] + 1); } else puts("NO"); } return 0; }