a1020 tree traversals

Suppose that all the keys in a binary tree are distinct positive integers. Given the postorder and inorder traversal sequences, you are supposed to output the level order traversal sequence of the corresponding binary tree.

Each input file contains one test case. For each case, the first line gives a positive integer N (≤30), the total number of nodes in the binary tree. The second line gives the postorder sequence and the third line gives the inorder sequence. All the numbers in a line are separated by a space.

For each test case, print in one line the level order traversal sequence of the corresponding binary tree. All the numbers in a line must be separated by exactly one space, and there must be no extra space at the end of the line.

7 
2 3 1 5 7 6 4 
1 2 3 4 5 6 7 

4 1 6 3 5 7 2

#include <bits/stdc++.h>
using namespace std;
const int max_n = 31;

struct node
{
    int data;
    node *lchild;
    node *rchild;
};

int in[max_n], post[max_n];
int N; 

node *create(int inL, int inR, int postL, int postR) //创建二叉树
{
    if (postL > postR)
        return nullptr;
    //构建根节点
    node *root = new node;
    root->data = post[postR];
    int k; //根节点在中序的位置
    for (k = inL; k <= inR; k++)
        if (in[k] == post[postR])
            break;
    int num_left = k - inL; //左子树结点的个数
    root->lchild = create(inL, k - 1, postL, postL + num_left - 1);
    root->rchild = create(k + 1, inR, postL + num_left, postR - 1);
    return root;
}

int num = 0; //已输出的结点的个数
void BFS(node *root)
{
    queue<node *> q;
    q.push(root);
    while (!q.empty())
    {
        node *temp = q.front();
        printf("%d", temp->data);
        q.pop();
        num++;
        if (num < N)
            printf(" ");
        if (temp->lchild != nullptr)
            q.push(temp->lchild);
        if (temp->rchild != nullptr)
            q.push(temp->rchild);
    }
}

int main()
{
    scanf("%d", &N);
    for (int i = 0; i < N; i++)
        scanf("%d", &post[i]);
    for (int i = 0; i < N; i++)
        scanf("%d", &in[i]);
    node *root = create(0, N - 1, 0, N - 1);
    BFS(root);
    return 0;
}