README.md

Binary Tree from Preorder and Inorder Traversal

by Pawan Kumar @jsartisan

Given two integer arrays preorder and inorder representing traversals of a binary tree:

• preorder contains the preorder traversal (root, left, right)
• inorder contains the inorder traversal (left, root, right)

Both arrays:

• Have the same length
• Contain unique values
• Represent the same binary tree

Construct and return the original binary tree.

Constraints:

• 1 ≤ array length ≤ 1000
• -1000 ≤ array values ≤ 1000
• Arrays contain unique values

Examples:

// Example 1:
//     1
//    /  \
//   2    3
//         \
//          4
const preorder1 = [1, 2, 3, 4];
const inorder1 = [2, 1, 3, 4];
console.log(buildTree(preorder1, inorder1));
// Output: [1, 2, 3, null, null, null, 4]

// Example 2:
//   1
const preorder2 = [1];
const inorder2 = [1];
console.log(buildTree(preorder2, inorder2));
// Output: [1]