萌新刚学OI，求助top序代码

B3644

#include<bits/stdc++.h>
using namespace std;
inline int read(){
    register int s=1,x=0;
    register char c=getchar();
    if(c=='-'){
        s=-1;
        c=getchar();
    }
    while(c<='9'&&c>='0'){
        x=(x<<3)+(x<<1)+(c^48);
        c=getchar();
    }
    return s*x;
}
inline void write(int x){
    if(x==0) return;
    if(x<0){
        putchar('-');
        x=~x-1;
    }
    write(x/10);
    putchar(x%10+'0');
}
struct Node{
    array<int,1000+10>child;
    array<int,1000+10>fa;
    int _top_=0,ru=0;
};
array<Node,1000+10>a;
int n;
void top_(){
    queue<int> q;
    array<bool,1000+10> vis;
    vis.fill(false); 
    for(int i=1;i<=n;++i){
        if(a[i].ru==0) q.push(i);
    }
    while(!q.empty()){
        auto now=q.front();
        write(now);
        putchar(' ');
        q.pop();
        if(vis.at(now)) continue;
        vis.at(now)=true;
        for(int i=1;i<=a[now]._top_;++i){
            --a[a[now].child[i]].ru;
            if(a[a[now].child[i]].ru==0){
                q.push(a[now].child[i]);
            }
        }
    }
}
int main(){
    n=read();
    for(int i=1;i<=n;++i){
        int tmp=read();
        while(tmp){
            a[i].child[++a[i]._top_]=tmp;
            a[tmp].fa[++a[tmp].ru]=i;
            tmp=read();
        }
    }
    top_();
}