UOJ 217 奇怪的线段树

http://uoj.ac/problem/217

题意就不X了，思路在这:

 

居然一开始把sap里面的mn设置为inf了，我是傻逼。。

#include<cstdio>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
#define inf 0x3f3f3f3f
int go[200005],first[200005],next[200005],flow[200005],op[200005],dis[200005],cnt[200005];
int tot,S,T,t,s,sz,son[200005],du[200005],n,nodes;
bool flag;
int read(){
    int t=0,f=1;char ch=getchar();
    while (ch<'0'||ch>'9'){if (ch=='-') f=-1;ch=getchar();}
    while ('0'<=ch&&ch<='9'){t=t*10+ch-'0';ch=getchar();}
    return t*f;
}
void insert(int x,int y,int z){
    tot++;
    go[tot]=y;
    next[tot]=first[x];
    first[x]=tot;
    flow[tot]=z;
}
void add(int x,int y,int z){
    insert(x,y,z);op[tot]=tot+1;
    insert(y,x,0);op[tot]=tot-1;
}
void add(int x,int y,int low,int high){
    int F=high-low;
    add(x,y,F);du[x]-=low;du[y]+=low;
}
int build(int l,int r,int op){
    int k=++sz;
    add(s,k,0,inf);add(k+2*n-1,t,0,inf);
    add(4*n-2+l,k,0,inf);if (op&&r<n) add(k+2*n-1,4*n-2+r+1,0,inf);
    if (!op) add(5*n-2+l,k,0,inf);
    if (!op&&r<n) add(k+2*n-1,5*n-2+r+1,0,inf);
    int x=read();
    if (l==r){
       son[k]=x;
       return x;
    }
    int mid=read();
    int p=build(l,mid,0),q=build(mid+1,r,1);
    if (p||q){
        if (!x) flag=0;
        son[k]=2;
        return 1;
    }
    return son[k]=x;
}
int dfs(int x,int f){
    if (x==T) return f;
    int mn=nodes,sum=0;
    for (int i=first[x];i;i=next[i]){
        int pur=go[i];
        if (dis[pur]+1==dis[x]&&flow[i]){
            int F=std::min(flow[i],f-sum);
            int save=dfs(pur,F);
            sum+=save;
            flow[i]-=save;
            flow[op[i]]+=save;
            if (sum==f||dis[S]>=nodes) return sum;
        }
        if (flow[i]) mn=std::min(mn,dis[pur]);
    }
    if (sum==0){
        cnt[dis[x]]--;
        if (cnt[dis[x]]==0){
           dis[S]=nodes;
        }else{
           dis[x]=mn+1;
           cnt[dis[x]]++;
        }
    }
    return sum;
}
int mxflow(){
    int res=0,tim=0;
    while (dis[S]<nodes){
        tim++;
        res+=dfs(S,inf);
    }
    return res;
}
int main(){
    n=read();
    s=0;t=6*n-1;
    flag=1;
    build(1,n,0);
    if (!flag) {puts("OwO");return 0;}
    for (int i=1;i<=sz;i++)
        if (son[i]==1)
            add(i,i+sz,1,inf);
        else 
        if (son[i]==2)
            add(i,i+sz,0,inf);
    S=t+1,T=S+1;nodes=T+1;    
    for (int i=s;i<=t;i++)
        if (du[i]>0) add(S,i,du[i]);
        else if (du[i]<0) add(i,T,-du[i]);    
    int ans1=mxflow();
    memset(dis,0,sizeof dis);
    memset(cnt,0,sizeof cnt);
    add(t,s,inf);
    int ans=mxflow();
    printf("%d\n",ans);
}