30. Substring with Concatenation of All Words.js

var flatten = function (root) {
  let head = null,
    curr = root;
  while (head != root) {
    if (curr.right === head) curr.right = null;
    if (curr.left === head) curr.left = null;
    if (curr.right) curr = curr.right;
    else if (curr.left) curr = curr.left;
    else (curr.right = head), (head = curr), (curr = root);
  }
  console.log(root);
};

// Definition for a binary tree node
class TreeNode {
  constructor(val, left, right) {
    this.val = val === undefined ? 0 : val;
    this.left = left === undefined ? null : left;
    this.right = right === undefined ? null : right;
  }
}

const root = new TreeNode(
  50,
  new TreeNode(
    25,
    new TreeNode(12, new TreeNode(6), new TreeNode(18)),
    new TreeNode(48, new TreeNode(32), new TreeNode(49))
  ),
  new TreeNode(
    75,
    new TreeNode(62, new TreeNode(61), new TreeNode(65)),
    new TreeNode(100, new TreeNode(99), new TreeNode(101))
  )
);

console.log(flatten(root));