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Grokking the Coding Interview Patterns in JavaScript

Build Binary Tree from Preorder and Inorder Traversal

Understand how to build a binary tree by using preorder and inorder traversal sequences. This lesson walks you through analyzing problem constraints and implementing a solution, helping you master tree depth-first search techniques in JavaScript.

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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
4
5

Try it yourself

Implement your solution in the following coding playground.

JavaScript
usercode > main.js
// Definition of a binary tree node

// class TreeNode {

//   constructor(data) {

//     this.data = data;

//     this.left = null;

//     this.right = null;

//   }

// }



import {TreeNode} from './ds_v1/BinaryTree.js';



function buildTree(pOrder, iOrder) {

    

    // Replace this placeholder return statement with your code

    return new TreeNode(-1);

}



export {buildTree};
Build Binary Tree from Preorder and Inorder Traversal