二叉搜索树的最近公共祖先

 public TreeNode commonAncestor (TreeNode root, int p, int q) {
        if (null == root) return null;
        if (root.val == p || root.val == q) return root;
        // 通过递归假设我们知道了运算结果 题目含义是不会出现重复节点
        TreeNode left = commonAncestor(root.left, p, q);
        TreeNode right = commonAncestor(root.right, p, q);
        if (left == null) return right;
        else if (right == null) return left;
        else return root;
    } 
    public int lowestCommonAncestor (TreeNode root, int p, int q) {
        // write code here
        return commonAncestor(root, p, q).val;
    }