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("\n");for(int i=0;i<(N);i++)\
 {for(int j=;j<(M);j++){\
 printf("%d",G[i][j]);}printf("\n");}
 //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 = ;
 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,-,sizeof dx);
     memset(dy,-,sizeof dy);
     for(int i=;i<=uN;i++)
     {
         if(Mx[i] == -)
         {
             Q.push(i);
             dx[i] = ;
         }
     }
     while(!Q.empty())
     {
         int u = Q.front();
         Q.pop();
         if(dx[u] > dis) break;
         int sz = G[u].size();
         for(int i=;i<sz;i++)
         {
             int v = G[u][i];
             if(dy[v] == -)
             {
                 dy[v] = dx[u] + ;
                 if(My[v] == -) dis = dy[v];
                 else
                 {
                     dx[My[v]] = dy[v] + ;
                     Q.push(My[v]);
                 }
             }
         }
     }
     return dis != INF;
 }
 bool DFS(int u)
 {
     int sz = G[u].size();
     for(int i=;i<sz;i++)
     {
         int v = G[u][i];
         if(!used[v] && dy[v] == dx[u]+)
         {
             used[v] = true;
             if(My[v] != - && dy[v] == dis) continue;
             if(My[v] == - || DFS(My[v]))
             {
                 My[v] = u;
                 Mx[u] = v;
                 return true;
             }
         }
     }
     return false;
 }
 int MaxMatch()
 {
     int res = ;
     memset(Mx,-,sizeof Mx);
     memset(My,-,sizeof My);
     while(searchP())
     {
         memset(used,false,sizeof used);
         for(int i=;i<=uN;i++)
         {
             if(Mx[i] == - && DFS(i)) res++;
         }
     }
     return res/;
 }

 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=;i<maxn;i++) G[i].clear();
         save.clear();
         for(int i=,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\n",match);
         for(int i=;i<=N;i++)
         {
             if(Mx[i] != -) st.insert(make_pair(i,Mx[i]));
         }
         int imp = ;
         for(auto it = st.begin();it != st.end();it++)
         {
             pair<int,int> cur = *it;
             //printf("delete [%d,%d]\n",cur.first,cur.second);
             for(int i=;i<maxn;i++) G[i].clear();
             for(int i=;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.\n",++cas,imp,match);
     }
 }