[BZOJ 1735] Muddy Fields

[题目链接]

         https://www.lydsy.com/JudgeOnline/problem.php?id=1735

[算法]

         二分图最小覆盖

[代码]

        

#include<bits/stdc++.h>
using namespace std;
#define MAXN 1010

struct edge
{
        int to,nxt;
} e[MAXN * MAXN];

int i,j,n,m,ans,cntx,cnty,tot;
char mp[MAXN][MAXN];
int x[MAXN][MAXN],y[MAXN][MAXN];
int match[MAXN],head[MAXN];
bool visited[MAXN];

inline void addedge(int u,int v)
{
        tot++;
        e[tot] = (edge){v,head[u]};
        head[u] = tot;
}
inline bool hungary(int u)
{
        int i,v;
        for (i = head[u]; i; i = e[i].nxt)
        {
                v = e[i].to;
                if (!visited[v])
                {
                        visited[v] = true;
                        if (!match[v] || hungary(match[v]))
                        {
                                match[v] = u;
                                return true;
                        }
                }
        }
        return false;
}

int main() 
{
        
        scanf("%d%d",&n,&m);
        for (i = 1; i <= n; i++) scanf("%s",mp[i] + 1);
        for (i = 1; i <= n; i++)
        {
                for (j = 1; j <= m; j++)
                {
                        if (mp[i][j] == '*')
                        {
                                x[i][j] = ++cntx;
                                while (j < m && mp[i][j + 1] == '*')
                                {
                                        j++;
                                        x[i][j] = cntx;        
                                }    
                        }                
                }
        }
        for (j = 1; j <= m; j++)
        {
                for (i = 1; i <= n; i++)
                {
                        if (mp[i][j] == '*')
                        {
                                y[i][j] = ++cnty;
                                while (i < n && mp[i + 1][j] == '*')
                                {
                                        i++;
                                        y[i][j] = cnty;
                                }
                        }
                }
        }
        for (i = 1; i <= n; i++)
        {
                for (j = 1; j <= m; j++)
                {
                        if (mp[i][j] == '*')
                                addedge(x[i][j],y[i][j]);        
                } 
        } 
        for (i = 1; i <= cntx; i++)
        {
                memset(visited,false,sizeof(visited));
                if (hungary(i)) ans++;
        }
        printf("%d\n",ans);
        
        return 0;
    
}