二叉树搜索最近公共祖先

public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q){
    if(root == null) return root;
    if(root == p || root = q) return root;
    //按照下面的图，认真将递归的过程在脑子中走一遍，可以帮助加深理解。
    TreeNode left = lowestCommonAncestor(root.left, p, q); 
    TreeNode right = lowestCommonAncestor(root.right, p, q);
    if(left != null && right != null){ // p, q 分属在左右两个子树上
        return root;
    } else if(left != null){
        return left;
    } else if(right != null){
        return right;
    }
    return null;
}