搜索DFS之城堡 The Castle

Posted 2020-12-16 soda-ma

题目

P1457 [USACO2.1]城堡 The Castle

思路

三遍DFS求解

代码

#include<bits/stdc++.h>
using namespace std;
int n,m;
const int maxn=50+5;
int a[maxn][maxn][maxn][maxn],large[maxn][maxn];
bool vis[maxn][maxn];
int cnt,Max,tot;
void dfs(int x,int y){
	if(vis[x][y])return ;
	cnt++;
	vis[x][y]=1;
	if(a[x][y][x+1][y])dfs(x+1,y);
	if(a[x][y][x][y+1])dfs(x,y+1);
	if(a[x][y][x-1][y])dfs(x-1,y);
	if(a[x][y][x][y-1])dfs(x,y-1);
	return;

}
void dfs2(int x,int y,int i,int j){
	if(vis[x][y])return ;
	large[x][y]=large[i][j];
	vis[x][y]=1;
	if(a[x][y][x+1][y])dfs2(x+1,y,i,j);
	if(a[x][y][x][y+1])dfs2(x,y+1,i,j);
	if(a[x][y][x-1][y])dfs2(x-1,y,i,j);
	if(a[x][y][x][y-1])dfs2(x,y-1,i,j);
	return;

}
bool dfs3(int i,int j,int k,int l){
	if(i==k&&j==l)return 1;
	if(vis[i][j])return 0;
	vis[i][j]=1;
	int xx=0;
	if(a[i][j][i+1][j])xx=xx|dfs3(i+1,j,k,l);
	if(a[i][j][i][j+1])xx=xx|dfs3(i,j+1,k,l);
	if(a[i][j][i-1][j])xx=xx|dfs3(i-1,j,k,l);
	if(a[i][j][i][j-1])xx=xx|dfs3(i,j-1,k,l);
	return xx;
}
bool judge(int i,int j,int k,int l){
	if(k==0||l==0||k>n||l>m)return 0;
	memset(vis,0,sizeof(vis));
	if(dfs3(i,j,k,l))return 0;
	return 1;
}
int main(){
	scanf("%d%d",&m,&n);
	int temp;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			scanf("%d",&temp);
			if(temp>=8)temp-=8;
			else a[i][j][i+1][j]=1;
			if(temp>=4)temp-=4;
			else a[i][j][i][j+1]=1;
			if(temp>=2)temp-=2;
			else a[i][j][i-1][j]=1;
			if(temp>=1)temp-=1;
			else a[i][j][i][j-1]=1;
		}
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			if(!vis[i][j]){
				tot++;
				cnt=0;
				dfs(i,j);
				large[i][j]=cnt;
				Max=max(Max,cnt);
			}
		}
	}
	memset(vis,0,sizeof(vis));
	printf("%d
%d
",tot,Max);
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			if(!vis[i][j]){
				dfs2(i,j,i,j);				
			}
		}
	}
	memset(vis,0,sizeof(vis));
	int ans=0;
	int aa=0,bb=0,rel=0;
	for(int j=1;j<=m;j++){
		for(int i=n;i>=1;i--){
			if(a[i][j][i-1][j]==0){
				if(judge(i,j,i-1,j)){
					if(ans<large[i][j]+large[i-1][j]){
						ans=large[i][j]+large[i-1][j];
					    aa=i,bb=j,rel=1;
					}
				}
			}
			if(a[i][j][i][j+1]==0){
				if(judge(i,j,i,j+1)){
					if(ans<large[i][j]+large[i][j+1]){
						ans=large[i][j]+large[i][j+1];
						aa=i,bb=j,rel=2;					
					}
				}
			}
		}
	}
	printf("%d
%d %d ",ans,aa,bb);
	if(rel==1)printf("N
");
	else printf("E
");
}