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
1 /*--------------------------------------------------------------------------------------*/ 2 3 #include <algorithm> 4 #include <iostream> 5 #include <cstring> 6 #include <ctype.h> 7 #include <cstdlib> 8 #include <cstdio> 9 #include <vector> 10 #include <string> 11 #include <queue> 12 #include <stack> 13 #include <cmath> 14 #include <set> 15 #include <map> 16 17 //debug function for a N*M array 18 #define debug_map(N,M,G) printf("\n");for(int i=0;i<(N);i++)\ 19 {for(int j=0;j<(M);j++){\ 20 printf("%d",G[i][j]);}printf("\n");} 21 //debug function for int,float,double,etc. 22 #define debug_var(X) cout<<#X"="<<X<<endl; 23 #define LL long long 24 const int INF = 0x3f3f3f3f; 25 const LL LLINF = 0x3f3f3f3f3f3f3f3f; 26 /*--------------------------------------------------------------------------------------*/ 27 using namespace std; 28 29 int N,M,E,T; 30 const int maxn = 1000; 31 vector <int> G[maxn]; 32 int uN; 33 int Mx[maxn],My[maxn]; 34 int dx[maxn],dy[maxn]; 35 int dis; 36 bool used[maxn]; 37 bool searchP() 38 { 39 queue<int> Q; 40 dis = INF; 41 memset(dx,-1,sizeof dx); 42 memset(dy,-1,sizeof dy); 43 for(int i=1;i<=uN;i++) 44 { 45 if(Mx[i] == -1) 46 { 47 Q.push(i); 48 dx[i] = 0; 49 } 50 } 51 while(!Q.empty()) 52 { 53 int u = Q.front(); 54 Q.pop(); 55 if(dx[u] > dis) break; 56 int sz = G[u].size(); 57 for(int i=0;i<sz;i++) 58 { 59 int v = G[u][i]; 60 if(dy[v] == -1) 61 { 62 dy[v] = dx[u] + 1; 63 if(My[v] == -1) dis = dy[v]; 64 else 65 { 66 dx[My[v]] = dy[v] + 1; 67 Q.push(My[v]); 68 } 69 } 70 } 71 } 72 return dis != INF; 73 } 74 bool DFS(int u) 75 { 76 int sz = G[u].size(); 77 for(int i=0;i<sz;i++) 78 { 79 int v = G[u][i]; 80 if(!used[v] && dy[v] == dx[u]+1) 81 { 82 used[v] = true; 83 if(My[v] != -1 && dy[v] == dis) continue; 84 if(My[v] == -1 || DFS(My[v])) 85 { 86 My[v] = u; 87 Mx[u] = v; 88 return true; 89 } 90 } 91 } 92 return false; 93 } 94 int MaxMatch() 95 { 96 int res = 0; 97 memset(Mx,-1,sizeof Mx); 98 memset(My,-1,sizeof My); 99 while(searchP()) 100 { 101 memset(used,false,sizeof used); 102 for(int i=1;i<=uN;i++) 103 { 104 if(Mx[i] == -1 && DFS(i)) res++; 105 } 106 } 107 return res/2; 108 } 109 110 vector <pair<int,int> > save; 111 set <pair<int,int> > st; 112 int cas; 113 int main() 114 { 115 while(~scanf("%d%d%d",&N,&M,&E)) 116 { 117 uN = N+M; 118 for(int i=0;i<maxn;i++) G[i].clear(); 119 save.clear(); 120 for(int i=0,a,b;i<E;i++) 121 { 122 scanf("%d%d",&a,&b); 123 G[a].push_back(N+b); 124 G[N+b].push_back(a); 125 save.push_back(make_pair(a,N+b)); 126 } 127 128 st.clear(); 129 int match = MaxMatch(); 130 //printf("MaxMatch:%d\n",match); 131 for(int i=1;i<=N;i++) 132 { 133 if(Mx[i] != -1) st.insert(make_pair(i,Mx[i])); 134 } 135 int imp = 0; 136 for(auto it = st.begin();it != st.end();it++) 137 { 138 pair<int,int> cur = *it; 139 //printf("delete [%d,%d]\n",cur.first,cur.second); 140 for(int i=0;i<maxn;i++) G[i].clear(); 141 for(int i=0;i<save.size();i++) if(save[i] != cur) 142 { 143 int a = save[i].first,b = save[i].second; 144 G[a].push_back(b); 145 G[b].push_back(a); 146 } 147 if(MaxMatch() < match) imp++; 148 } 149 printf("Board %d have %d important blanks for %d chessmen.\n",++cas,imp,match); 150 } 151 }
