题面
https://www.luogu.org/problemnew/show/P2825
题解
水题
二分图匹配的经典模型。
对于硬石头,拆点。
// luogu-judger-enable-o2 #include<cstdio> #include<iostream> #include<cstring> #include<vector> #include<queue> #define ri register int #define N 505000 #define INF 1000000007 #define T (n+m+1) using namespace std; int n,m,han[100][100],lie[100][100]; vector<int> to,w,ed[N]; int cur[N],d[N],tn,tm; char g[100][100]; void add_edge(int u,int v,int w1,int w2) { to.push_back(v); w.push_back(w1); ed[u].push_back(to.size()-1); to.push_back(u); w.push_back(w2); ed[v].push_back(to.size()-1); } bool bfs() { queue<int> q; memset(d,0x3f,sizeof(d)); d[0]=0; q.push(0); while (!q.empty()) { int x=q.front(); q.pop(); for (ri i=0,l=ed[x].size();i<l;i++) { int e=ed[x][i]; if (w[e] && d[x]+1<d[to[e]]) { d[to[e]]=d[x]+1; q.push(to[e]); } } } return d[T]<=1000000; } int dfs(int x,int limit) { if (x==T || !limit) return limit; int tot=0; for (ri &i=cur[x];i<ed[x].size();i++) { int e=ed[x][i]; if (d[to[e]]==d[x]+1 && w[e]) { int f=dfs(to[e],min(limit,w[e])); if (!f) continue; w[e]-=f; w[1^e]+=f; tot+=f; limit-=f; if (!limit) return tot; } } return tot; } int dinic() { int ret=0; while (bfs()) { memset(cur,0,sizeof(cur)); ret+=dfs(0,INF); } return ret; } void init() { int tn=0,tm=0; for (ri i=1;i<=n;i++) { ++tn; for (ri j=1;j<=m;j++) { han[i][j]=tn; if (g[i][j]=='#') tn++; } } for (ri i=1;i<=m;i++) { ++tm; for (ri j=1;j<=n;j++) { lie[j][i]=tm; if (g[j][i]=='#') tm++; } } n=tn; m=tm; return; } void makegraph() { for (ri i=1;i<=n;i++) add_edge(0,i,1,0); for (ri i=1;i<=m;i++) add_edge(n+i,T,1,0); for (ri i=1;i<=tn;i++) for (ri j=1;j<=tm;j++) if (g[i][j]=='*') add_edge(han[i][j],n+lie[i][j],1,0); } int main() { scanf("%d %d",&n,&m); tn=n; tm=m; for (ri i=1;i<=n;i++) scanf("%s",g[i]+1); init(); makegraph(); printf("%d ",dinic()); }