此种方法会RE 6个点 但是当我数组改为son[maxn][2]时，可以AC

#include<bits/stdc++.h>
using namespace std; 
const int maxn=1000005;

int fa[maxn],son[2][maxn];

void dfs_q(int now)
{
	if(now==0)return ;
	cout<<now<<" ";
	dfs_q(son[1][now]);
	dfs_q(son[2][now]);
}

void dfs_z(int now)
{
	if(now==0)return ;
	dfs_z(son[1][now]);
	cout<<now<<" ";
	dfs_z(son[2][now]);
//	return ;
}

void dfs_h(int now)
{
	if(now==0)return ;
	dfs_h(son[1][now]);
	dfs_h(son[2][now]);
	cout<<now<<" ";
}
int main()
{
	int n;
//	std::ios::sync_with_stdio(false);
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		int l,r;
		cin>>l>>r;
		fa[l]=i,fa[r]=i;
		son[1][i]=l;
		son[2][i]=r;
	}
	dfs_q(1);
	cout<<endl;
	dfs_z(1);
	cout<<endl;
	dfs_h(1);
	return 0;
}