HDU1281-棋盘游戏-二分图匹配

先跑一个二分图匹配，然后一一删去匹配上的边，看能不能达到最大匹配数，不能这条边就是重要边

/*--------------------------------------------------------------------------------------*/

#include <algorithm>
#include <iostream>
#include <cstring>
#include <ctype.h>
#include <cstdlib>
#include <cstdio>
#include <vector>
#include <string>
#include <queue>
#include <stack>
#include <cmath>
#include <set>
#include <map>

//debug function for a N*M array
#define debug_map(N,M,G) printf("
");for(int i=0;i<(N);i++)
{for(int j=0;j<(M);j++){
printf("%d",G[i][j]);}printf("
");}
//debug function for int,float,double,etc.
#define debug_var(X) cout<<#X"="<<X<<endl;
#define LL long long
const int INF = 0x3f3f3f3f;
const LL LLINF = 0x3f3f3f3f3f3f3f3f;
/*--------------------------------------------------------------------------------------*/
using namespace std;

int N,M,E,T;
const int maxn = 1000;
vector <int> G[maxn];
int uN;
int Mx[maxn],My[maxn];
int dx[maxn],dy[maxn];
int dis;
bool used[maxn];
bool searchP()
{
    queue<int> Q;
    dis = INF;
    memset(dx,-1,sizeof dx);
    memset(dy,-1,sizeof dy);
    for(int i=1;i<=uN;i++)
    {
        if(Mx[i] == -1)
        {
            Q.push(i);
            dx[i] = 0;
        }
    }
    while(!Q.empty())
    {
        int u = Q.front();
        Q.pop();
        if(dx[u] > dis) break;
        int sz = G[u].size();
        for(int i=0;i<sz;i++)
        {
            int v = G[u][i];
            if(dy[v] == -1)
            {
                dy[v] = dx[u] + 1;
                if(My[v] == -1) dis = dy[v];
                else
                {
                    dx[My[v]] = dy[v] + 1;
                    Q.push(My[v]);
                }
            }
        }
    }
    return dis != INF;
}
bool DFS(int u)
{
    int sz = G[u].size();
    for(int i=0;i<sz;i++)
    {
        int v = G[u][i];
        if(!used[v] && dy[v] == dx[u]+1)
        {
            used[v] = true;
            if(My[v] != -1 && dy[v] == dis) continue;
            if(My[v] == -1 || DFS(My[v]))
            {
                My[v] = u;
                Mx[u] = v;
                return true;
            }
        }
    }
    return false;
}
int MaxMatch()
{
    int res = 0;
    memset(Mx,-1,sizeof Mx);
    memset(My,-1,sizeof My);
    while(searchP())
    {
        memset(used,false,sizeof used);
        for(int i=1;i<=uN;i++)
        {
            if(Mx[i] == -1 && DFS(i)) res++;
        }
    }
    return res/2;
}

vector <pair<int,int> > save;
set <pair<int,int> > st;
int cas;
int main()
{
    while(~scanf("%d%d%d",&N,&M,&E))
    {
        uN = N+M;
        for(int i=0;i<maxn;i++) G[i].clear();
        save.clear();
        for(int i=0,a,b;i<E;i++)
        {
            scanf("%d%d",&a,&b);
            G[a].push_back(N+b);
            G[N+b].push_back(a);
            save.push_back(make_pair(a,N+b));
        }

        st.clear();
        int match = MaxMatch();
        //printf("MaxMatch:%d
",match);
        for(int i=1;i<=N;i++)
        {
            if(Mx[i] != -1) st.insert(make_pair(i,Mx[i]));
        }
        int imp = 0;
        for(auto it = st.begin();it != st.end();it++)
        {
            pair<int,int> cur = *it;
            //printf("delete [%d,%d]
",cur.first,cur.second);
            for(int i=0;i<maxn;i++) G[i].clear();
            for(int i=0;i<save.size();i++) if(save[i] != cur)
            {
                int a = save[i].first,b = save[i].second;
                G[a].push_back(b);
                G[b].push_back(a);
            }
            if(MaxMatch() < match) imp++;
        }
        printf("Board %d have %d important blanks for %d chessmen.
",++cas,imp,match);
    }
}