【BZOJ1064】[Noi2008]假面舞会【DFS】【分类讨论】

【题目链接】

以为要分层图...没思路，去看题解，膜拜proverbs【proverbs的题解】

/* Footprints In The Blood Soaked Snow */
#include <cstdio>
#include <algorithm>

using namespace std;

const int maxn = 100005, maxm = 1000005;

int n, m, head[maxn], cnt, ans1, ans2, dis[maxn];
bool vis[maxn];

struct _edge {
	int v, w, next;
} g[maxm << 1];

inline int iread() {
	int f = 1, x = 0; char ch = getchar();
	for(; ch < '0' || ch > '9'; ch = getchar()) f = ch == '-' ? -1 : 1;
	for(; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';
	return f * x;
}

inline void add(int u, int v, int w) {
	g[cnt] = (_edge){v, w, head[u]};
	head[u] = cnt++;
}

inline int intabs(int x) {
	return x > 0 ? x : -x;
}

inline int gcd(int a, int b) {
	for(; b; b ^= a ^= b ^= a %= b);
	return a;
}

inline void dfs(int x) {
	vis[x] = 1;
	for(int i = head[x]; ~i; i = g[i].next)
		if(!vis[g[i].v]) dis[g[i].v] = dis[x] + g[i].w, dfs(g[i].v);
		else ans1 = gcd(ans1, intabs(dis[x] + g[i].w - dis[g[i].v]));
}

int mx, mi;

inline void tree(int x) {
	vis[x] = 0;
	mx = max(mx, dis[x]); mi = min(mi, dis[x]);
	for(int i = head[x]; ~i; i = g[i].next) if(vis[g[i].v])
		dis[g[i].v] = dis[x] + g[i].w, tree(g[i].v);
}

int main() {
	n = iread(); m = iread();
	for(int i = 1; i <= n; i++) head[i] = -1; cnt = 0;

	for(int i = 1; i <= m; i++) {
		int u = iread(), v = iread();
		add(u, v, 1); add(v, u, -1);
	}

	for(int i = 1; i <= n; i++) if(!vis[i]) dfs(i);
	if(ans1) for(ans2 = 3; ans2 <= ans1 && ans1 % ans2; ans2++);
	else {
		ans2 = 3;
		for(int i = 1; i <= n; i++) if(vis[i]) {
			mx = mi = dis[i] = 0;
			tree(i);
			ans1 += mx - mi + 1;
		}
	}

	if(ans1 < 3) ans1 = ans2 = -1;
	printf("%d %d\n", ans1, ans2);
	return 0;
}