construct-binary-tree-from-preorder-and-inorder-traversal.js

/**Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, construct and return the binary tree. */
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {number[]} preorder
 * @param {number[]} inorder
 * @return {TreeNode}
 */
 var buildTree = function(preorder, inorder) {
    if (preorder.length === 0 || inorder.length === 0) {
      return null;
    }
    
    let root = new TreeNode(preorder[0]);
    let mid = inorder.indexOf(preorder[0]);
    
    root.left = buildTree(preorder.slice(1, mid + 1), inorder.slice(0, mid));
    root.right = buildTree(preorder.slice(mid + 1), inorder.slice(mid + 1))
    return root;                   
      
  };