【Codeforces 723D】Lakes in Berland （dfs）

海洋包围的小岛，岛内的有湖，'.'代表水，'*'代表陆地，给出的n*m的地图里至少有k个湖，求填掉面积尽量少的水，使得湖的数量正好为k。

dfs找出所有水联通块，判断一下是否是湖（海水区非湖）。将湖按面积排序，若湖的数量为cnt，填掉前cnt-k个湖。

http://codeforces.com/problemset/problem/723/D

Examples

input

5 4 1*****..*******.*..**

output

1*****..*********..**

input

3 3 0****.****

output

1*********

#include<bits/stdc++.h>
using namespace std;
int n,m,k;
char a[55][55];
bool vis[55][55];
int dx[6]={0,0,1,-1};
int dy[6]={1,-1,0,0};int num,cnt,islake;
int ans;
struct lake{int x,y;int num;int id;
}lk[3600];
bool cmp(lake a,lake b){return a.num<b.num;
}
void dfs(int x,int y){vis[x][y]=1;num++;if(x==0||x==n-1||y==0||y==m-1)islake=0;for(int i=0;i<4;i++){int nx=x+dx[i],ny=y+dy[i];if(nx>=0&&nx<n&&ny<m&&ny>=0&&a[nx][ny]=='.'&&!vis[nx][ny])dfs(nx,ny);}
}
void fil(int x,int y,int id){vis[x][y]=1;ans++;a[x][y]='*';for(int i=0;i<4;i++){int nx=x+dx[i],ny=y+dy[i];if(nx>=0&&nx<n&&ny<m&&ny>=0&&a[nx][ny]=='.'&&!vis[nx][ny])fil(nx,ny,id);}
}
int main(){scanf("%d%d%d",&n,&m,&k);for(int i=0;i<n;i++)scanf(" %s",a[i]);for(int i=0;i<n;i++)for(int j=0;j<m;j++)if(!vis[i][j]&&a[i][j]=='.'){num=0;islake=1;dfs(i,j);if(islake)lk[cnt++]=(lake){i,j,num,cnt};}memset(vis,0,sizeof vis);sort(lk,lk+cnt,cmp);for(int l=0;l<cnt-k;l++)for(int i=0;i<n;i++)for(int j=0;j<m;j++)if(i==lk[l].x&&j==lk[l].y)fil(i,j,lk[l].id);printf("%d\n",ans);for(int i=0;i<n;i++)printf("%s\n",a[i]);
}

转载于:https://www.cnblogs.com/flipped/p/5930002.html

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