HDU 1269 迷宫城堡 最大强连通图题解

寻找一个迷宫是否是仅仅有一个最大强连通图。

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

參考资料：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; }