lowest-common-ancestor-of-a-binary-tree.js

/**
 * 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) {
  // 后续遍历
  if (!root || p === root || q === root) return root;

  const left = lowestCommonAncestor(root.left, p, q);
  const right = lowestCommonAncestor(root.right, p, q);

  if (left && right) {
    return root;
  } else if (!left && right) {
    return right;
  } else if (left && !right) {
    return left;
  } else {
    // left == null && right == null
    return null;
  }
};