HDU 1269 迷宫城堡 最大强连通图题解

寻找一个迷宫是否是只有一个最大强连通图。

使用Tarjan算法去求解，经典算法，必须要学习好，要自己创造出来是十分困难的了。

参考资料：https://www.byvoid.com/blog/scc-tarjan/

const int N = 10001;vector<int> gra[N];stack<int> stk;bool inStack[N];int dfsNum[N];int backTrackNum[N];int cur, sum;int n, m;void Tarjan(int u){inStack[u] = true;dfsNum[u] = backTrackNum[u] = ++cur;stk.push(u);for (int i = 0; i < (int)gra[u].size(); i++){int v = gra[u][i];if (!dfsNum[v]) Tarjan(v), backTrackNum[u] = backTrackNum[v] < backTrackNum[u]? backTrackNum[v] : backTrackNum[u];else if (inStack[v]) backTrackNum[u] = backTrackNum[v] < backTrackNum[u]? backTrackNum[v] : backTrackNum[u];}if (backTrackNum[u] == dfsNum[u]){++sum;while (stk.size()){int v = stk.top(); stk.pop();inStack[v] = false;if (u == v) break;}}}void solveTarjan(){sum = cur = 0;memset(dfsNum, 0, sizeof(dfsNum));for (int i = 1; i <= n; i++){if (!dfsNum[i]) Tarjan(i);}}void initGraph(){int a, b;for (int i = 1; i <= n; i++) gra[i].clear();//别忘了清空for (int i = 0; i < m; i++){scanf("%d %d", &a, &b);gra[a].push_back(b);}}int main(){while (scanf("%d %d", &n, &m) && n){initGraph();solveTarjan();if (sum == 1) puts("Yes");else puts("No");}return 0;}