def dfs(self, root, k1, k2, ret):
        if not root:
            return

        if k1 < root.val:
            self.dfs(root.right, k1, k2, ret)
        elif root.val > k2:
            self.dfs(root.left, k1, k2, ret)
        else:
            self.dfs(root.left, k1, k2, ret)
            ret.append(root.val)
            self.dfs(root.right, k1, k2, ret)
dataset/ETHPy150Open algorhythms/LintCode/Search Range in Binary Search Tree.py/Solution.dfs/swapped operands of `<`