算法导论求最大流这一节还没看过，下午看了下，参照了大牛的代码模仿写了Ford-Fulkerson+BFS过了...
1 /* 2 3 ID: hubiao cave 4 5 PROG: ditch 6 7 LANG: C++ 8 9 */ 10 11 12 13 14 #include<iostream> 15 16 #include<fstream> 17 18 #include<cstring> 19 #include<queue> 20 #include<deque> 21 22 using namespace std; 23 24 25 26 int E[201][201]; 27 int m,n; 28 bool visited[201]; 29 int prenumber; 30 queue<pair<int,int> > intqueue; 31 deque<pair<int,int> >intde; 32 33 void BFS(); 34 void PreBFS(); 35 int main() 36 37 { 38 39 40 ifstream fin("ditch.in"); 41 42 ofstream fout("ditch.out"); 43 44 fin>>n>>m; 45 for(int i=1;i<=n;i++) 46 { 47 int x,y,z; 48 fin>>x>>y>>z; 49 E[x][y]+=z; 50 } 51 int ans=0; 52 for(;;) 53 { 54 PreBFS(); 55 BFS(); 56 if(prenumber==0) 57 break; 58 int min=2111111111; 59 60 int pre=intde.back().second; 61 do 62 { 63 while(intde.back().second!=pre) 64 intde.pop_back(); 65 pair<int,int>cur=intde.back(); 66 intde.pop_back(); 67 if(E[cur.first][cur.second]<min&&cur.first!=0) 68 min=E[cur.first][cur.second]; 69 if(cur.first!=0) 70 intde.push_front(cur); 71 pre=cur.first; 72 }while(pre!=0); 73 74 ans+=min; 75 while(!intde.empty()) 76 { 77 pair<int,int> pii=intde.front(); 78 intde.pop_front(); 79 E[pii.first][pii.second]-=min; 80 E[pii.second][pii.first]+=min; 81 } 82 } 83 84 fout<<ans<<endl; 85 return 0; 86 87 88 } 89 90 void BFS() 91 { 92 intqueue.push(make_pair(0,1)); 93 while(!intqueue.empty()) 94 { 95 pair<int,int> cur=intqueue.front(); 96 if(visited[cur.second]) 97 { 98 intqueue.pop(); 99 continue; 100 } 101 if(cur.second==m) 102 { 103 prenumber=cur.first; 104 intde.push_back(cur); 105 return; 106 } 107 visited[cur.second]=true; 108 intde.push_back(cur); 109 intqueue.pop(); 110 for(int i=1;i<=m;i++) 111 { 112 if(E[cur.second][i]&&!visited[i]) 113 { 114 intqueue.push(make_pair(cur.second,i)); 115 } 116 } 117 } 118 } 119 120 void PreBFS() 121 { 122 while(!intqueue.empty()) 123 { 124 intqueue.pop(); 125 } 126 intde.clear(); 127 prenumber=0; 128 memset(visited,0,sizeof(visited)); 129 130 }