[BZOJ2929][POI1999]洞穴攀行（网络流）

题目描述

题解

代码

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
using namespace std;

const int max_n=205;
const int max_N=max_n+2;
const int max_m=max_n*max_n;
const int max_e=max_m*2;
const int INF=1e9;

int n,m,N,x;
int tot,point[max_N],next[max_e],v[max_e],remain[max_e];
int deep[max_N],num[max_N],last[max_N],cur[max_N];
int maxflow;
queue <int> q;

inline void addedge(int x,int y,int cap){
++tot; next[tot]=point[x]; point[x]=tot; v[tot]=y; remain[tot]=cap;
++tot; next[tot]=point[y]; point[y]=tot; v[tot]=x; remain[tot]=0;
}
inline void bfs(int t){
for (int i=1;i<=N;++i) deep[i]=N;
deep[t]=0;
for (int i=1;i<=N;++i) cur[i]=point[i];
while (!q.empty()) q.pop();
q.push(t);

while (!q.empty()){
int now=q.front(); q.pop();
for (int i=point[now];i!=-1;i=next[i])
if (deep[v[i]]==N&&remain[i^1]){
deep[v[i]]=deep[now]+1;
q.push(v[i]);
}
}
}
inline int addflow(int s,int t){
int now=t,ans=INF;
while (now!=s){
ans=min(ans,remain[last[now]]);
now=v[last[now]^1];
}
now=t;
while (now!=s){
remain[last[now]]-=ans;
remain[last[now]^1]+=ans;
now=v[last[now]^1];
}
return ans;
}
inline void isap(int s,int t){
bfs(t);
for (int i=1;i<=N;++i) ++num[deep[i]];

int now=s;
while (deep[s]<N){
if (now==t){
maxflow+=addflow(s,t);
now=s;
}

bool has_find=false;
for (int i=cur[now];i!=-1;i=next[i])
if (deep[v[i]]+1==deep[now]&&remain[i]){
has_find=true;
cur[now]=i;
last[v[i]]=i;
now=v[i];
break;
}

if (!has_find){
int minn=N-1;
for (int i=point[now];i!=-1;i=next[i])
if (remain[i]) minn=min(minn,deep[v[i]]);
if (!(--num[deep[now]])) break;
num[deep[now]=minn+1]++;
cur[now]=point[now];
if (now!=s) now=v[last[now]^1];
}
}
}

int main(){
tot=-1;
memset(point,-1,sizeof(point));
memset(next,-1,sizeof(next));

scanf("%d",&n);
N=n+2;
for (int i=1;i<n;++i){
scanf("%d",&m);
for (int j=1;j<=m;++j){
scanf("%d",&x);
if (i==1||x==n) addedge(1+i,1+x,1);
else addedge(1+i,1+x,INF);
}
}
addedge(1,2,INF);
addedge(N-1,N,INF);
isap(1,N);
printf("%d\n",maxflow);
}