[luogu1971 NOI2011] 兔兔与蛋蛋游戏 (二分图博弈)

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Solution

补一篇二分图博弈

这个博客写的很详细qwq： https://www.cnblogs.com/maijing/p/4703094.html

Code

//By Menteur_Hxy
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#define F(i,a,b) for(register int i=(a);i<=(b);i++)
#define E(i,u) for(register int i=head[u],v;i;i=nxt[i])
#define add(a,b) nxt[++cnt]=head[a],to[cnt]=b,head[a]=cnt
using namespace std;

const int N=50;
int mv[5]={0,1,0,-1,0};
int n,m,tot,top,tim,X,Y,cnt;
bool mp[N][N],jud[2010],ban[N*N];
int head[N*N],to[N*N*N*N],nxt[N*N*N*N],vis[N*N];
int id[N][N],mat[N*N],ans[1010];
char ch[N];

bool dfs(int u) {
	if(ban[u]) return false;
	E(i,u) if(vis[(v=to[i])]!=tim&&!ban[v]) {
		vis[v]=tim;
		if(!mat[v] || dfs(mat[v])) {
			mat[v]=u;mat[u]=v;
			return true;
		}
	}
	return false;
}

int main() {
	cin>>n>>m;
	F(i,1,n) {
		scanf("%s",ch+1);
		F(j,1,m) if(ch[j]=='O') mp[i][j]=0;
			else if(ch[j]=='X') mp[i][j]=1;
			else if(ch[j]=='.') mp[i][j]=1,X=i,Y=j;
	}
	F(i,1,n) F(j,1,m) id[i][j]=++tot;
	F(i,1,n) F(j,1,m) if(mp[i][j]) F(k,0,3) {
		int x=i+mv[k],y=j+mv[k+1];
		if(mp[x][y]||x<1||x>n||y<1||y>m) continue;
		add(id[i][j],id[x][y]); add(id[x][y],id[i][j]);
	}
	F(i,1,n) F(j,1,m) if(mp[i][j]) ++tim,dfs(id[i][j]);
	int q; cin>>q;
	F(i,1,q+q) {
		int now=id[X][Y],v=mat[now];
		ban[now]=true;//!!!
		if(v) {
			mat[now]=mat[v]=0;
			++tim; jud[i]=!dfs(v);
		}
		cin>>X>>Y;
	}
	F(i,1,q) if(jud[i+i-1]&jud[i+i]) ans[++top]=i;
	printf("%d\n",top);
	F(i,1,top) printf("%d\n",ans[i]);
	return 0;
}