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Build Binary Tree from Preorder and Inorder Traversal

Explore how to build a binary tree by using preorder and inorder traversal arrays. Learn to analyze the relationship between these traversals and implement an algorithm to reconstruct the tree, improving your understanding of tree structures and depth-first search techniques.

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Statement

Create a binary tree from two integer arrays, pOrder and iOrder, where pOrder represents a preorder traversal of a binary tree, and iOrder represents an inorder traversal of the same tree.

Constraints:

  • 1≤1 \leq pOrder.length, iOrder.length ≤1000\leq1000
  • iOrder.length ==== pOrder.length
  • −1000≤-1000 \leq pOrder[i], iOrder[i] ≤1000\leq 1000
  • pOrder and iOrder consist of unique values.
  • Each value of iOrder also appears in pOrder and vice versa.

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps us to check if you’re solving the correct problem:

Build Binary Tree from Preorder and Inorder Traversal

1.

Select the correct binary tree constructed from preorder and inorder traversal:

preorder = [1, 12, 15, 6, 9, 5, 2]

inorder = [15, 12, 6, 1, 5, 9, 2]

A.
    1
   /  \
  12   9
 / \  / \
15  6 5  2
B.
    12
   /  \
  1    9
 / \  / \
15  6 5  2
C.
    15
   /  \
  12   9
 / \  / \
1  6 5   2
D.
    9
   /  \
  1   12
 / \  / \
15  6 5  2
1 / 2

Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
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5

Try it yourself

Implement your solution in the following coding playground.

Java
usercode > Solution.java
import java.util.*;
import ds_v1.BinaryTree.TreeNode;
// Definiton of a binary tree node class
// class TreeNode<T> {
//     T data;
//     TreeNode<T> left;
//     TreeNode<T> right;
//     TreeNode(T data) {
//         this.data = data;
//         this.left = null;
//         this.right = null;
//     }
// }
public class Solution {
    
    public static TreeNode<Integer> buildTree(int[] pOrder, int[] iOrder) {
        // Replace this placeholder return statement with your code
        return new TreeNode<Integer>(-1);
    }
}
Build Binary Tree from Preorder and Inorder Traversal