Codeforces_723_D

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

dfs找出每个湖，保存坐标和大小，按大小排序，填充湖即可，注意湖的数量最多会有1250个。

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<cmath>
#define INF 0x3f3f3f3f
using namespace std;

int n,m,k,dir[][2] = {-1,0,0,-1,1,0,0,1},ok,cnt = 0,sizee,vis[55][55] = {0};
char mp[55][55];

struct lake
{
    int x,y,cnt;
}l[1300];

bool cmp(struct lake a,struct lake b)
{
    return a.cnt < b.cnt;
}

void dfs1(int x,int y)
{
    vis[x][y] = 1;
    sizee++;
    for(int i = 0;i < 4;i++)
    {
        int xx = x+dir[i][0],yy = y+dir[i][1];
        if(xx < 0 || yy < 0 || xx >= n || yy >= m)
        {
            ok = 0;
            continue;
        }
        if(mp[xx][yy] == '*' || vis[xx][yy])    continue;
        
        dfs1(xx,yy);
    }
}

void dfs2(int x,int y)
{
    mp[x][y] = '*';
    for(int i = 0;i < 4;i++)
    {
        int xx = x+dir[i][0],yy = y+dir[i][1];
        if(xx < 0 || yy < 0 || xx >= n || yy >= m)    continue;
        if(!vis[xx][yy])    continue;
        vis[xx][yy] = 0;
        dfs2(xx,yy);
    }
}

int main()
{
    scanf("%d%d%d",&n,&m,&k);
    getchar();
    int x = 0;
    while(gets(mp[x++]));
    for(int i = 0;i < n;i++)
    {
        for(int j = 0;j < m;j++)
        {
            sizee = 0;
            ok = 1;
            if(mp[i][j] == '.' && !vis[i][j])
            {
                dfs1(i,j);
                if(ok)
                {
                    l[cnt].x = i;
                    l[cnt].y = j;
                    l[cnt++].cnt = sizee;
                }
            }
        }
    }
    sort(l,l+cnt,cmp);
    int endd = cnt-k,ans = 0;
    for(int i = 0;i < endd;i++)
    {
        ans += l[i].cnt;
        dfs2(l[i].x,l[i].y);
    }
    printf("%d
",ans);
    for(int i = 0;i < n;i++)    puts(mp[i]);
    return 0;
}