AcWing 372. 棋盘覆盖

给n*n的方格图铺满1*2 的长条，且某些位置不能铺，问最多能放多少个长条

#include <iostream>
#include<queue> 
#include <vector>
#include <cstring>
using namespace std;
 const int N =110 ,M=N*N;
 #define int long long
 vector<int> g[M];
 
 void add_(int x,int y){
 	g[x].push_back(y);
 }
 int n,vis[M],mch[M];
 
 bool dfs(const int x,const int cas){
 	if(vis[x]==cas) return 0; 
 	vis[x]=cas;
 	for(int i=0;i<g[x].size();i++){
 		int y=g[x][i];
 		if(mch[y]==0||dfs(mch[y],cas)){
 			mch[y]=x; return 1;
 		}
 	}
 	return 0;
 }
 
 int K,ban[N][N],b[N][N],id[N][N];
 int D[5][2]={{1,0},{-1,0},{0,1},{0,-1}};
 
 bool OK(int x,int y){
 	return x>0&&x<=n&&y>0&&y<=n;
 }
 signed main(){
 	int i,j,x,y;
 	cin>>n>>K;
 	for(i=1;i<=K;i++){
 		cin>>x>>y;
 		ban[x][y]=1;
 	}
 	for(i=1;i<=n;i++)
 	 for(j=1;j<=n;j++){
 	 	if(ban[i][j]) continue; 
 	 	
 	 	if((i+j)&1) b[i][j]=1; else b[i][j]=0;
 	 	id[i][j]=(i-1)*n+j;
 	 	
 	 	for(int k=0;k<4;k++){
 	 		int xx=D[k][0]+i,yy=D[k][1]+j; 
 	 		 if(OK(xx,yy)==0) continue; 
 	 		if(ban[xx][yy]) continue;
 	 		int id2=(xx-1)*n+yy;
 	 		
 	 		if(b[xx][yy]!=b[i][j]) add_(id[i][j],id2);
 	 	}
 	 }
 	 
 	 int ans=0;
 	for(i=1;i<=n;i++) 
 	 for(j=1;j<=n;j++){
 	 	if(b[i][j] &&ban[i][j]==0&& dfs(id[i][j],id[i][j])) ans++;
 	 }
 	
 	cout<<ans<<endl;
 }