图论专题A (网络流)

需要跑多遍的网络流，一个是注意bfs的时候deep不能用memset赋值，一个是每一次网络流的过程都会带来wei和cur的改变

#include "bits/stdc++.h"
using namespace std;
typedef long long LL;
const LL MAX=1e6+5;
LL n,m,s,t,ans;
LL tot,head[MAX],adj[MAX*6],wei[MAX*6],nxt[MAX*6];
LL deep[MAX],cur[MAX];
inline LL read(){
    LL an=0,x=1;char c=getchar();
    while (c<'0' || c>'9') {if (c=='-') x=-1;c=getchar();}
    while (c>='0' && c<='9') {an=(an<<3)+(an<<1)+c-'0';c=getchar();}
    return an*x;
}
void addedge(LL u,LL v,LL w){
    tot++;adj[tot]=v,wei[tot]=w,nxt[tot]=head[u],head[u]=tot;
}
bool bfs(){
    LL i,j,u;
    for (i=1;i<=n;i++) deep[i]=1e9+10;
    deep[s]=0;
    queue <LL> q;
    while (!q.empty()) q.pop();
    q.push(s);
    while (!q.empty()){
        u=q.front();q.pop();
        for (i=head[u];i;i=nxt[i]){
            if (deep[adj[i]]>1e9 && wei[i]>0)
                deep[adj[i]]=deep[u]+1,q.push(adj[i]);
        }
    }
    return deep[t]<1e9;
}
LL dfs(LL x,LL flo){
    if (x==t || flo==0) return flo;
    LL j;
    for (LL &i=cur[x];i;i=nxt[i])
        if (deep[adj[i]]==deep[x]+1 && wei[i]>0){
            j=dfs(adj[i],min(flo,wei[i]));
            if (j) return wei[i]-=j,wei[i^1]+=j,j;
        }
    return 0;
}
int main(){
    freopen ("a.in","r",stdin);freopen ("a.out","w",stdout);
    LL i,j,u,v,w;
    n=read();m=read();
    LL flow=0,dd;ans=1e9;
    tot=1;
    for (i=1;i<=m;i++){
        u=read();v=read();
        addedge(u,v,1);
        addedge(v,u,1);
    }
    for (i=1;i<=n;i++) cur[i]=head[i];
    for (t=2;t<=n;t++){
        s=1;
        for (i=1;i<=tot;i++) wei[i]=1;
        flow=0;
        while (bfs()){
            for (i=1;i<=n;i++) cur[i]=head[i];
            while (dd=dfs(s,1e9)) flow+=dd;
        }
        ans=min(ans,flow);
    }
    printf("%lld",ans);
    return 0;
}