【codeforces 723D】【DFS (Floodfill)】D. Lakes in Berland【把多于k的连通块填起来,最外面的连通块直接忽视】

本文介绍了一个关于地图上湖泊的算法问题,目标是最小化填土操作来达到指定数量的独立湖泊。通过DFS搜索算法确定湖泊边界并计算面积,采用贪心策略选择最小的湖泊进行填充。

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描述:

D. Lakes in Berland
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

The map of Berland is a rectangle of the size n × m, which consists of cells of size 1 × 1. Each cell is either land or water. The map is surrounded by the ocean.

Lakes are the maximal regions of water cells, connected by sides, which are not connected with the ocean. Formally, lake is a set of water cells, such that it's possible to get from any cell of the set to any other without leaving the set and moving only to cells adjacent by the side, none of them is located on the border of the rectangle, and it's impossible to add one more water cell to the set such that it will be connected with any other cell.

You task is to fill up with the earth the minimum number of water cells so that there will be exactly k lakes in Berland. Note that the initial number of lakes on the map is not less than k.

Input

The first line of the input contains three integers nm and k (1 ≤ n, m ≤ 500 ≤ k ≤ 50) — the sizes of the map and the number of lakes which should be left on the map.

The next n lines contain m characters each — the description of the map. Each of the characters is either '.' (it means that the corresponding cell is water) or '*' (it means that the corresponding cell is land).

It is guaranteed that the map contain at least k lakes.

Output

In the first line print the minimum number of cells which should be transformed from water to land.

In the next n lines print m symbols — the map after the changes. The format must strictly follow the format of the map in the input data (there is no need to print the size of the map). If there are several answers, print any of them.

It is guaranteed that the answer exists on the given data.

Examples
input
5 4 1
****
*..*
****
**.*
..**
output
1
****
*..*
****
****
..**
input
3 3 0
***
*.*
***
output
1
***
***
***
Note

In the first example there are only two lakes — the first consists of the cells (2, 2) and (2, 3), the second consists of the cell (4, 3). It is profitable to cover the second lake because it is smaller. Pay attention that the area of water in the lower left corner is not a lake because this area share a border with the ocean.


题意:

把多于k的连通块填起来,最外面的连通块直接忽视

思路:

裸的dfs,Floodfill的思想,先把边缘的海隔离化,然后dfs出每个联通块的size,最后贪心填充最小的

代码:

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

char s[55][55];
int n, m, k, adj, cnt, tot;
int vis[55][55];
int dx[] = { -1, 1, 0, 0}, dy[] = {0, 0, -1, 1};
int f[55 * 55];
vector <pair <int, int> > v;

void dfs(int x, int y) {
  cnt ++;
  vis[x][y] = tot;//把对应的区域染色
  if (x == 0 || x == n - 1 || y == 0 || y == m - 1) adj = 1;
  for (int i = 0; i < 4; i ++) {
    int nx = x + dx[i], ny = y + dy[i];
    if (nx < 0 || nx >= n || ny < 0 || ny >= m || s[nx][ny] != '.' || vis[nx][ny]) continue;
    dfs(nx, ny);
  }
}

int main() {
  scanf("%d %d %d", &n, &m, &k);
  for (int i = 0; i < n; i ++)
    scanf("%s", s[i]);
  for (int i = 0; i < n; i ++)
    for (int j = 0; j < m; j ++) {
      if (s[i][j] == '.' && ! vis[i][j]) {
        cnt = adj = 0;
        ++ tot;
        dfs(i, j);
        if (! adj) v.push_back({cnt, tot});
      }
    }
  sort(v.begin(), v.end());
  int sum = 0;
  for (int i = v.size(), j = 0; i > k; i --, j ++) {
    f[v[j].second] = 1; sum += v[j].first;
  }
  cout << sum << endl;
  for (int i = 0; i < n; i ++) {
    for (int j = 0; j < m; j ++) {
      if (f[vis[i][j]]) putchar('*');
      else putchar(s[i][j]);
    }
    puts("");
  }
  return 0;
}



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