PKU 2226 - Muddy Fields (最小点覆盖)

题意

用最少的木板覆盖。

思路

很有意思的建图。横着标号，然后竖着标号，建边，求最小点覆盖。

代码

  
  
  
  

   
   
   
   
#include <cstdio>
   
   
   
   
#include <stack>
   
   
   
   
#include <set>
   
   
   
   
#include <iostream>
   
   
   
   
#include <string>
   
   
   
   
#include <vector>
   
   
   
   
#include <queue>
   
   
   
   
#include <functional>
   
   
   
   
#include <cstring>
   
   
   
   
#include <algorithm>
   
   
   
   
#include <cctype>
   
   
   
   
#include <string>
   
   
   
   
#include <map>
   
   
   
   
#include <cmath>
   
   
   
   
#define LL long long
   
   
   
   
#define SZ(x) (int)x.size()
   
   
   
   
#define Lowbit(x) ((x) & (-x))
   
   
   
   
#define MP(a, b) make_pair(a, b)
   
   
   
   
#define MS(arr, num) memset(arr, num, sizeof(arr))
   
   
   
   
#define PB push_back
   
   
   
   
#define F first
   
   
   
   
#define S second
   
   
   
   
#define ROP freopen("input.txt", "r", stdin);
   
   
   
   
#define MID(a, b) (a + ((b - a) >> 1))
   
   
   
   
#define LC rt << 1, l, mid
   
   
   
   
#define RC rt << 1|1, mid + 1, r
   
   
   
   
#define LRT rt << 1
   
   
   
   
#define RRT rt << 1|1
   
   
   
   
#define BitCount(x) __builtin_popcount(x)
   
   
   
   
const double PI = acos(-1.0);
   
   
   
   
const int INF = 0x3f3f3f3f;
   
   
   
   
using namespace std;
   
   
   
   
const int MAXN = 2000 + 10;
   
   
   
   
const int MOD = 1e9 + 7;
   
   
   
   
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
   
   
   
   

   
   
   
   
typedef pair<int, int> pii;
   
   
   
   
typedef vector<int>::iterator viti;
   
   
   
   
typedef vector<pii>::iterator vitii;
   
   
   
   

   
   
   
   
struct EDGE
   
   
   
   
{
   
   
   
   
 int from, to, cap;
   
   
   
   
};
   
   
   
   

   
   
   
   
struct HUNGARY
   
   
   
   
{
   
   
   
   
 int vis[MAXN], link[MAXN], head[MAXN], next[MAXN * MAXN];
   
   
   
   
 vector<EDGE> edges;
   
   
   
   

   
   
   
   
 void init()
   
   
   
   
 {
   
   
   
   
 edges.clear();
   
   
   
   
 MS(head, -1); MS(link, -1);
   
   
   
   
 }
   
   
   
   

   
   
   
   
 int solve(int nrem)
   
   
   
   
 {
   
   
   
   
 int res = 0;
   
   
   
   
 for (int i = 1; i <= nrem; i++)
   
   
   
   
 {
   
   
   
   
 MS(vis, 0);
   
   
   
   
 res += DFS(i);
   
   
   
   
 }
   
   
   
   
 return res;
   
   
   
   
 }
   
   
   
   

   
   
   
   
 void add_edge(int from, int to)
   
   
   
   
 {
   
   
   
   
 EDGE a = {from, to};
   
   
   
   
 edges.PB(a);
   
   
   
   
 int m = SZ(edges);
   
   
   
   
 next[m - 1] = head[from];
   
   
   
   
 head[from] = m - 1;
   
   
   
   
 }
   
   
   
   

   
   
   
   
 int DFS(int u)
   
   
   
   
 {
   
   
   
   
 for (int i = head[u]; i != -1; i = next[i])
   
   
   
   
 {
   
   
   
   
 int v = edges[i].to;
   
   
   
   
 if (!vis[v])
   
   
   
   
 {
   
   
   
   
 vis[v] = 1;
   
   
   
   
 if (link[v] == -1 || DFS(link[v]))
   
   
   
   
 {
   
   
   
   
 link[v] = u;
   
   
   
   
 return 1;
   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
 return 0;
   
   
   
   
 }
   
   
   
   
}hun;
   
   
   
   

   
   
   
   
char mp[MAXN][MAXN];
   
   
   
   
int num[MAXN][MAXN];
   
   
   
   

   
   
   
   
int main()
   
   
   
   
{
   
   
   
   
 //ROP;
   
   
   
   
 int row, col, i, j;
   
   
   
   
 while (~scanf("%d%d", &row, &col))
   
   
   
   
 {
   
   
   
   
 hun.init();
   
   
   
   
 for (i = 1; i <= row; i++) scanf("%s", mp[i] + 1);
   
   
   
   
 int cnt = 0;
   
   
   
   
 for (i = 1; i <= row; i++)
   
   
   
   
 {
   
   
   
   
 for (j = 1; j<= col; j++)
   
   
   
   
 if (mp[i][j] == '*') num[i][j] = (mp[i][j] == mp[i][j - 1] ? cnt : ++cnt);
   
   
   
   
 }
   
   
   
   
 cnt = 0;
   
   
   
   
 for (i = 1; i <= col; i++)
   
   
   
   
 {
   
   
   
   
 for (j = 1; j <= row; j++)
   
   
   
   
 {
   
   
   
   
 if (mp[j][i] == '*')
   
   
   
   
 {
   
   
   
   
 if (mp[j][i] != mp[j - 1][i]) cnt++;
   
   
   
   
 hun.add_edge(cnt, num[j][i]);
   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
 printf("%d\n", hun.solve(cnt));
   
   
   
   
 }
   
   
   
   
 return 0;
   
   
   
   
}