Lowest Common Ancestor of a Binary Tree

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param root: The root of the binary search tree.
     * @param A: A TreeNode in a Binary.
     * @param B: A TreeNode in a Binary.
     * @return: Return the least common ancestor(LCA) of the two nodes.
     */

    /*
自底向上遍历结点，一旦遇到结点等于p或者q，则将其向上传递给它的父结点。父结点会判断它的左右子树是否都包含其中一个结点，
如果是，则父结点一定是这两个节点p和q的LCA，传递父结点到root。
如果不是，我们向上传递其中的包含结点p或者q的子结点，或者NULL(如果子结点不包含任何一个)。该方法时间复杂度为O(N)。
    */
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode A, TreeNode B) {
        // write your code here
        if (root == null) {
            return null;
        }

         if (root == A || root == B) {
            return root;
        }
        

        TreeNode left = lowestCommonAncestor(root.left,A,B);
        TreeNode right = lowestCommonAncestor(root.righ,A,B);
        
       
        if (left != null && righ != null) {
            return root;
        }

         return left!= null ? left:right;
    }
}