//Recursive solution
//Time: O(n), 13ms
//Space: O(h)
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root == null) return null;//Base case 1: Not found
        if(root == p) return p;//Base Case 2: Found one
        if(root == q) return q;
        TreeNode left = lowestCommonAncestor(root.left, p, q);
        TreeNode right = lowestCommonAncestor(root.right, p, q);
        if(left != null && right != null) {//Case 1, p and q are in different branch of root
            return root;
        }
        if(left == null) {//Case 2, p and q are both in right subtree OR Case 4, p and q are not decedents of the root
            return right;
        } else {//Case 3, p and q are both in left subtree
            return left;
        }
    }
}
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */