【BZOJ2208】[Jsoi2010]连通数【BFS/DFS】【SCC】

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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;}

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