【BZOJ2208】[Jsoi2010]连通数【BFS/DFS】【SCC】

http://www.lydsy.com/JudgeOnline/problem.php?id=2208

tarjan缩点然后dp。

但是发现点数才2000...BFS可过。

边数是n^2，不是n << 1...= =

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

using namespace std;

const int maxn = 2005, maxq = 10000;

int n, head[maxn], cnt, vis[maxn], clo, q[maxq];

struct _edge {
	int v, next;
} g[maxn * maxn];

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) {
	g[cnt] = (_edge){v, head[u]};
	head[u] = cnt++;
}

inline int bfs(int x) {
	int h = 0, t = 0; vis[q[t++] = x] = clo;
	int ans = 0;
	while(h != t) {
		int u = q[h++]; ans++;
		for(int i = head[u]; ~i; i = g[i].next) if(vis[g[i].v] != clo) {
			vis[g[i].v] = clo;
			q[t++] = g[i].v;
		}
	}
	return ans;
}

char str[maxn];

int main() {
	n = iread();
	for(int i = 1; i <= n; i++) head[i] = -1; cnt = clo = 0;
	for(int i = 1; i <= n; i++) {
		scanf("%s", str + 1);
		for(int j = 1; j <= n; j++) if(str[j] == '1') add(i, j);
	}

	int ans = 0;
	for(int i = 1; i <= n; i++) {
		clo++;
		ans += bfs(i);
	}

	printf("%d\n", ans);
	return 0;
}