水水水……放一下模版就好了：
1 /* 2 P1761 运输问题 3 一般增广路算法 4 Author:GodCowC 5 */ 6 #include <iostream> 7 #include <cstdio> 8 #include <cctype> 9 #include <cmath> 10 #define MAXN 101 11 #define INF 100000000 12 using namespace std; 13 int readint() 14 { 15 int ans=0; 16 char c; 17 while (!isdigit(c=getchar())); 18 do 19 { 20 ans=ans*10+c-'0'; 21 c=getchar(); 22 } while (isdigit(c)); 23 return ans; 24 } 25 int n; 26 int s,t; 27 struct Node 28 { 29 int pre; 30 bool del; 31 Node(int p=0,bool d=false):pre(p),del(d){} 32 }; 33 struct Edge 34 { 35 int flow,cap; 36 Edge(int f=0,int c=0):flow(f),cap(c){} 37 }; 38 Node argpath[MAXN]; 39 Edge graph[MAXN][MAXN]; 40 void init() 41 { 42 for (int i=1;i<=n;i++) 43 argpath[i]=Node(0,0); 44 } 45 int find() 46 { 47 int i(s); 48 while (i<=n && (!argpath[i].pre || argpath[i].del)) 49 i++; 50 return (i>n?0:i); 51 } 52 bool ford(int& change) 53 { 54 init(); 55 argpath[s].pre=s; 56 do 57 { 58 int i=find(); 59 if (!i) 60 return true; 61 for (int j=1;j<=n;j++) 62 { 63 if (argpath[j].pre) 64 continue; 65 argpath[j].pre=(graph[i][j].flow<graph[i][j].cap?i:argpath[j].pre); 66 argpath[j].pre=(graph[j][i].flow?-i:argpath[j].pre); 67 } 68 argpath[i].del=true; 69 } while (!argpath[t].pre); 70 int now=t; 71 change=INF; 72 do 73 { 74 int j=now; 75 now=abs(argpath[j].pre); 76 change=min(change, 77 (argpath[j].pre<0?graph[j][now].flow:graph[now][j].cap-graph[now][j].flow)); 78 } while (now!=s); 79 return false; 80 } 81 void fulkerson(int change) 82 { 83 int now=t; 84 do 85 { 86 int j=now; 87 now=abs(argpath[j].pre); 88 if (argpath[j].pre<0) 89 graph[j][now].flow-=change; 90 else 91 graph[now][j].flow+=change; 92 } while (now!=s); 93 } 94 void putmaxflow() 95 { 96 int ans=0; 97 for (int i=1;i<=n;i++) 98 ans+=graph[i][t].flow; 99 cout<<ans<<endl; 100 } 101 int main() 102 { 103 n=readint(); 104 s=1,t=n; 105 for (int i=1;i<=n;i++) 106 for (int j=1;j<=n;j++) 107 graph[i][j]=Edge(0,readint()); 108 do 109 { 110 int change=0; 111 bool ok=ford(change); 112 if (ok) 113 { 114 putmaxflow(); 115 break; 116 } 117 else 118 fulkerson(change); 119 } while (true); 120 return 0; 121 }
1 /* 2 P1761 运输问题 3 预流推进算法 4 Author:GodCowC 5 */ 6 #include <iostream> 7 #include <cstdio> 8 #include <cctype> 9 #include <cmath> 10 #include <algorithm> 11 #define MAXN 101 12 #define INF 100000000 13 using namespace std; 14 int readint() 15 { 16 int ans=0; 17 char c; 18 while (!isdigit(c=getchar())); 19 do 20 { 21 ans=ans*10+c-'0'; 22 c=getchar(); 23 } while (isdigit(c)); 24 return ans; 25 } 26 int n,d[MAXN],e[MAXN],s,t; 27 int c[MAXN][MAXN],p[MAXN][MAXN]; 28 int check() 29 { 30 int j=0; 31 for (int i=2;i<n;i++) 32 j+=e[i]; 33 return j; 34 } 35 int find() 36 { 37 for (int i=2;i<n;i++) 38 if (e[i]!=0) 39 return i; 40 } 41 int push(int x) 42 { 43 int i,j; 44 for (i=1;i<=n;i++) 45 if (d[x]==d[i]+1 && c[x][i]!=0) 46 break; 47 if (i<=n) 48 { 49 j=min(e[x],c[x][i]); 50 e[x]-=j; 51 c[x][i]-=j; 52 if (i!=t) 53 e[i]+=j; 54 c[i][x]+=j; 55 } 56 else 57 d[x]++; 58 if (j==0) 59 d[x]++; 60 return 0; 61 } 62 int main() 63 { 64 int sum=0; 65 n=readint(); 66 for (int i=1;i<=n;i++) 67 for (int j=1;j<=n;j++) 68 c[i][j]=readint(); 69 for (int i=1;i<=n;i++) 70 for (int j=1;j<=n;j++) 71 { 72 if (c[i][j]>0) 73 p[i][j]=1; 74 else if (i==j) 75 p[i][j]=0; 76 else 77 p[i][j]=32767; 78 } 79 for (int k=1;k<=n;k++) 80 for (int i=1;i<=n;i++) 81 for (int j=1;j<=n;j++) 82 p[i][j]=min(p[i][j],p[i][k]+p[k][j]); 83 s=1,t=n; 84 for (int i=1;i<=n;i++) 85 d[i]=p[i][t]; 86 for (int i=1;i<=n;i++) 87 { 88 e[i]=c[s][i]; 89 sum+=e[i]; 90 c[i][s]=c[s][i]; 91 } 92 d[s]=n; 93 while (check()) 94 { 95 int i=find(); 96 push(i); 97 } 98 cout<<sum-e[s]<<endl; 99 return 0; 100 }