A1020. Tree Traversals (25)

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.

Input Specification:

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.

Output Specification:

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.

Sample Input:

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

Sample Output:

4 1 6 3 5 7 2

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <string.h>
#include <math.h>
#include <algorithm>
#include <string>
#include <stack> 
#include <queue>
using namespace std;
struct node{
    int data;
    node * left;
    node *right;
}; 
const int maxn=50;
int in[maxn];
int post[maxn];
node * create(int a,int b,int c,int d)
{
    if(a>b)return NULL;
    node * newnode=new node;
    newnode->data=post[b];
    //后序最后一个节点
    int k=0;
    for(;k+c<=d;k++)
    {
        if(in[k+c]==post[b])
        {
            break;
        }
    }
    newnode->left=create(a,a+k-1,c,c+k-1);
    newnode->right=create(a+k,b-1,c+k+1,d);
    return newnode;        
}
 int n;
int BFS(node * root )
{
    queue<node *> q;
    int num=0;
    q.push(root);
    while(!q.empty())
    {
        node * temp=q.front();
        q.pop();
        printf("%d",temp->data);
        num++;
        if(num<n)printf(" ");
        if(temp->left!=NULL)q.push(temp->left);
        if(temp->right!=NULL)q.push(temp->right);
    }
}

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;
}