网络流入门题目

Program P1273;
Var
   n,m,i,j,x,y,p,level:longint;
   map,f:array[1..400,1..400] of longint;
   list:array[0..400,0..400] of longint;
   queue:array[1..400] of longint;
   b:array[1..400] of boolean;
   d,e:array[1..400] of longint;
function min(a,b:longint):longint;
begin
   if a<b then exit(a) else exit(b);
end;
function max(a,b:longint):longint;
begin
   if a>b then exit(a) else exit(b);
end;
procedure dijstra;
var
   h,t,i:longint;
begin
   queue[1]:=n;
   b[n]:=true;
   h:=1;
   t:=1;
   while h<=t do
   begin
      for i:=1 to n-1 do
         if (map[i,queue[h]]>0) and (not(b[i])) then
         begin
            inc(t);
            queue[t]:=i;
            b[i]:=true;
            d[i]:=d[queue[h]]+1;
         end;
      inc(h);
   end;
   d[1]:=n+1;
end;
procedure push(i,j:longint);
var
   flow:longint;
begin
   flow:=min(map[i,j]-f[i,j],e[i]);

   if (e[j]=0) and (j<>1) and (j<>n) then
   begin
      inc(list[d[j],0]);
      list[d[j],list[d[j],0]]:=j;
      level:=max(level,d[j]);
   end;

   dec(e[i],flow);
   inc(e[j],flow);
   inc(f[i,j],flow);
   f[j,i]:=-f[i,j];
end;
procedure relable(i:longint);
var
   j,minj:longint;
begin
   minj:=maxlongint;
   for j:=1 to n do
      if (map[i,j]-f[i,j]>0) and (b[j]) then
         minj:=min(minj,d[j]);
   d[i]:=minj+1;

   level:=d[i];
   list[level,0]:=1;
   list[level,1]:=i;
end;
procedure sa;
var
   i,j,minj:longint;
   tag:boolean;
begin
   dijstra;
   level:=0;
   for i:=1 to n do
      if (map[1,i]>0) and (b[i]) then
      begin
         dec(e[1],map[1,i]);
         inc(e[i],map[1,i]);
         inc(f[1,i],map[1,i]);
         f[i,1]:=-f[1,i];
         inc(list[d[i],0]);
         list[d[i],list[d[i],0]]:=i;
         level:=max(level,d[i]);
      end;
   while (level>0) do
   begin
      i:=list[level,list[level,0]];
      dec(list[level,0]);
      while (level>0) and (list[level,0]=0) do dec(level);

      for j:=1 to n do
         if (map[i,j]-f[i,j]>0) and (d[i]=d[j]+1) and (b[j]) then
         begin
            push(i,j);
            if e[i]=0 then break;
         end;
      if e[i]>0 then relable(i);
   end;
end;
begin
   while not eof do
   begin
      fillchar(map,sizeof(map),0);
      fillchar(f,sizeof(f),0);
      fillchar(d,sizeof(d),0);
      fillchar(b,sizeof(b),false);
      fillchar(list,sizeof(list),0);
      fillchar(e,sizeof(e),0);
      readln(m,n);
      for i:=1 to m do
      begin
         readln(x,y,p);
         inc(map[x,y],p);
      end;
      sa;
      writeln(e[n]);
   end;
end.

Sap：

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<functional>
#include<cstdlib>
#include<cstring>
using namespace std;
#define MAXN (200000+10)
#define MAXNnode (200000+10)
#define MAXedge (200000+10)
#define INF (2139062143)
int n,m,size,edge[MAXedge],pre[MAXNnode],next[MAXedge],weight[MAXedge],s,t;
int un(int p){return (p%2)?(p+1):p-1;}
void addedge(int u,int v,int w)
{
     edge[++size]=v;weight[size]=w;
     next[size]=pre[u];pre[u]=size;
     edge[++size]=u;weight[size]=0;
     next[size]=pre[v];pre[v]=size;
}
int q[MAXN*10],d[MAXN*2],pre2[MAXN],cnt[MAXN];
void spfa()
{
    int head=1,tail=1;
    memset(d,127,sizeof(d));
    q[1]=t;d[t]=0;
    while (head<=tail)
    {
        int &u=q[head];
        for (int p=pre[u];p;p=next[p])
        {
            int &v=edge[p];
            if (d[v]>d[u]+1)
            {
               d[v]=d[u]+1;
               q[++tail]=v;
               cnt[d[v]]++;
            }
        }
        head++;
    }

}
int relable(int u)
{
    int minj=n;
    for (int p=pre[u];p;p=next[p])
        if (weight[p]&&d[edge[p]]!=INF) minj=min(minj,d[edge[p]]+1);
    return minj;
}
long long sap()
{
     spfa();
     int now=s;
	 long long nowflow=INF,maxflow=0;
     while (1)
     {
         int flag=0;
         for (int p=pre[now];p;p=next[p])
         {
             int &v=edge[p];
             if (weight[p]&&d[v]==d[now]-1)
             {
                 flag=v;
                 pre2[v]=p;
                 now=v;
                 break;
             }
         }
         if (flag)
         {
            if (now==t)
            {
               nowflow=INF;
               for (int p=now;p!=s;p=edge[un(pre2[p])])
                   nowflow=min(nowflow,(long long )weight[pre2[p]]);
               maxflow+=nowflow;
               for (int p=now;p!=s;p=edge[un(pre2[p])])
               {
                   weight[pre2[p]]-=nowflow;
                   weight[un(pre2[p])]+=nowflow;
               }
               now=s;
               memset(pre2,0,sizeof(pre2));
            }
         }
         else
         {
             if (--cnt[d[now]]==0) break;
             d[now]=relable(now);
             cnt[d[now]]++;
             if (now!=s) now=edge[un(pre2[now])];
     	}
     }
     return maxflow;
}
int main()
{
	while (scanf("%d%d",&m,&n)==2)
	{
	    memset(pre,0,sizeof(pre));
	    memset(next,0,sizeof(next));
	    memset(edge,0,sizeof(edge));
	    memset(weight,0,sizeof(weight));
    	    memset(cnt,0,sizeof(cnt));
	    size=0; s=1;t=n;
            for (int i=1;i<=m;i++)
	    {
    	        int u,v,w;
        	cin>>u>>v>>w;
  	        addedge(u,v,w);
    	    }
        if (m==0) cout<<'0'<<endl;
	    else cout<<sap()<<endl;
	}
	return 0;
}