EOJ 2575 Separate Connections [2009年研究生机试]

带花树开花算法

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <vector>
#include <cmath>
#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
#include <map>
#include <queue>
 
using namespace std;
 
#define MAXN 250
#define MAXE MAXN*MAXN*2
#define SET(a,b) memset(a,b,sizeof(a))
deque<int> Q;
bool g[MAXN][MAXN],inque[MAXN],inblossom[MAXN];
int match[MAXN],pre[MAXN],base[MAXN];

int findancestor(int u,int v)
{
    bool inpath[MAXN]= {false};
    while(1)
    {
        u=base[u];
        inpath[u]=true;
        if(match[u]==-1)break;
        u=pre[match[u]];
    }
    while(1)
    {
        v=base[v];
        if(inpath[v])return v;
        v=pre[match[v]];
    }
}
 
void reset(int u,int anc)
{
    while(u!=anc)
    {
        int v=match[u];
        inblossom[base[u]]=1;
        inblossom[base[v]]=1;
        v=pre[v];
        if(base[v]!=anc)pre[v]=match[u];
        u=v;
    }
}
 
void contract(int u,int v,int n)
{
    int anc=findancestor(u,v);
    SET(inblossom,0);
    reset(u,anc);
    reset(v,anc);
    if(base[u]!=anc)pre[u]=v;
    if(base[v]!=anc)pre[v]=u;
    for(int i=1; i<=n; i++)
        if(inblossom[base[i]])
        {
            base[i]=anc;
            if(!inque[i])
            {
                Q.push_back(i);
                inque[i]=1;
            }
        }
}
 
bool dfs(int S,int n)
{
    for(int i=0; i<=n; i++)pre[i]=-1,inque[i]=0,base[i]=i;
    Q.clear();
    Q.push_back(S);
    inque[S]=1;
    while(!Q.empty())
    {
        int u=Q.front();
        Q.pop_front();
        for(int v=1; v<=n; v++)
        {
            if(g[u][v]&&base[v]!=base[u]&&match[u]!=v)
            {
                if(v==S||(match[v]!=-1&&pre[match[v]]!=-1))contract(u,v,n);
                else if(pre[v]==-1)
                {
                    pre[v]=u;
                    if(match[v]!=-1)Q.push_back(match[v]),inque[match[v]]=1;
                    else
                    {
                        u=v;
                        while(u!=-1)
                        {
                            v=pre[u];
                            int w=match[v];
                            match[u]=v;
                            match[v]=u;
                            u=w;
                        }
                        return true;
                    }
                }
            }
        }
    }
    return false;
}
 
int solve(int n)
{
    SET(match,-1);
    int ans=0;
    for(int i=1; i<=n; i++)
        if(match[i]==-1&&dfs(i,n))
            ans++;
    return ans;
}
 
int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    int ans;
    int n,m;
    char tmp[30];
    scanf("%d",&n);
    while(n--)
    {
        ans=0;
        memset(g,0,sizeof(g));
        scanf("%d",&m);
        for(int i=1;i<=m;i++)
        {
            scanf("%s",tmp+1);
            for(int j=1;j<=m;j++)
            {
                if(tmp[j]=='Y')
                {
                    g[i][j]=g[j][i]=1;
                }
            }
        }
        ans=solve(m);
        printf("%d\n",ans*2);
    }
 
    return 0;
}