253. Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”

Example

Example 1:

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6.

Example 2:

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */

/**
 * @param {TreeNode} root
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {TreeNode}
 */
var lowestCommonAncestor = function (root, p, q) {
  let pPath = [];
  let qPath = [];
  let path = [];
  function travel(node) {
    if (node) {
      path.push(node);
      if (node === p) {
        pPath = path.slice(0);
      }
      if (node === q) {
        qPath = path.slice(0);
      }
      travel(node.left);
      travel(node.right);
      path.pop();
    }
  }
  travel(root);

  let i = 0;
  for (; i < pPath.length || i < qPath.length; i++) {
    if (pPath[i] !== qPath[i]) {
      break;
    }
  }
  return pPath[i - 1];
};