[bzoj1797] [Ahoi2009]Mincut 最小割

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 const int maxn=4023,maxm=60233;
 7 struct zs{
 8     int too,pre,flow;
 9 }e[maxm<<1];int tot,last[maxn];
10 short dis[maxn],dl[maxn];
11 int st[maxn],top,dfn[maxn],low[maxn],tim,bel[maxn],cnt;
12 bool ins[maxn];
13 int i,j,k,n,m,s,t;
14  
15 int ra;char rx;
16 inline int read(){
17     rx=getchar(),ra=0;
18     while(rx<‘0‘||rx>‘9‘)rx=getchar();
19     while(rx>=‘0‘&&rx<=‘9‘)ra*=10,ra+=rx-48,rx=getchar();return ra;
20 }
21 inline bool bfs(){
22     memset(dis,0,(n+1)<<1);
23     int l=0,r=1,i,now;dl[1]=s,dis[s]=1;
24     while(l<r&&!dis[t])
25         for(i=last[now=dl[++l]];i;i=e[i].pre)if(e[i].flow&&!dis[e[i].too])
26             dl[++r]=e[i].too,dis[e[i].too]=dis[now]+1;
27     return dis[t];
28 }
29 inline int min(int a,int b){return a<b?a:b;}
30 int dfs(int x,int mx){
31     if(x==t)return mx;
32     int i,used=0,w;
33     for(i=last[x];i;i=e[i].pre)if(e[i].flow&&dis[e[i].too]==dis[x]+1){
34         w=dfs(e[i].too,min(e[i].flow,mx-used));if(w){
35             e[i].flow-=w,e[i^1].flow+=w,used+=w;
36             if(used==mx)return mx;
37         }
38     }
39     dis[x]=0;return used;
40 }
41  
42 void tarjan(int x){
43     int i;
44     dfn[x]=low[x]=++tim,ins[x]=1,st[++top]=x;
45     for(i=last[x];i;i=e[i].pre)if(e[i].flow){
46         if(!dfn[e[i].too])tarjan(e[i].too),low[x]=min(low[x],low[e[i].too]);
47         else if(ins[e[i].too])low[x]=min(low[x],dfn[e[i].too]);
48     }
49     if(low[x]==dfn[x]){
50         cnt++;
51         while(st[top]!=x)bel[st[top]]=cnt,ins[st[top]]=0,top--;
52         bel[x]=cnt,ins[x]=0,top--;
53     }
54 }
55  
56 inline void insert(int a,int b,int c){
57     e[++tot].too=b,e[tot].flow=c,e[tot].pre=last[a],last[a]=tot,
58     e[++tot].too=a,e[tot].flow=0,e[tot].pre=last[b],last[b]=tot;
59 }
60  
61 int main(){
62     n=read(),m=read(),s=read(),t=read(),tot=1;
63     for(i=1;i<=m;i++)j=read(),k=read(),insert(j,k,read());
64     while(bfs())dfs(s,1002333333);
65     for(i=1;i<=n;i++)if(!dfn[i])tarjan(i);
66     for(i=2;i<=tot;i+=2){
67         if(e[i].flow){puts("0 0");continue;}
68         if(bel[e[i^1].too]!=bel[e[i].too])printf("1 ");else printf("0 ");
69         if(bel[e[i^1].too]==bel[s]&&bel[e[i].too]==bel[t])puts("1");else puts("0");
70     }
71     return 0;
72 }
73