236. Lowest Common Ancestor of a Binary Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root,TreeNode p,TreeNode q) {
      if (root == null) return null;
      if (root == p || root == q) return root;
      TreeNode left = lowestCommonAncestor(root.left,p,q);
      TreeNode right = lowestCommonAncestor(root.right,q);
      if ( left != null && right != null) return root;
      if( left == null && right == null) return null;
      
      return left != null ? left : right; 
        
    }
}