# ---
# title: 501. Find Mode in Binary Search Tree
# id: problem501
# author: Tian Jun
# date: 2020-10-31
# difficulty: Easy
# categories: Tree
# link: <https://leetcode.com/problems/find-mode-in-binary-search-tree/description/>
# hidden: true
# ---
# 
# Given a binary search tree (BST) with duplicates, find all the
# [mode(s)](https://en.wikipedia.org/wiki/Mode_\(statistics\)) (the most
# frequently occurred element) in the given BST.
# 
# Assume a BST is defined as follows:
# 
#   * The left subtree of a node contains only nodes with keys **less than or equal to** the node's key.
#   * The right subtree of a node contains only nodes with keys **greater than or equal to** the node's key.
#   * Both the left and right subtrees must also be binary search trees.
# 
# 
# 
# For example:  
# Given BST `[1,null,2,2]`,
# 
#     
#     
#        1
#         \
#          2
#         /
#        2
#     
# 
# 
# 
# return `[2]`.
# 
# **Note:** If a tree has more than one mode, you can return them in any order.
# 
# **Follow up:** Could you do that without using any extra space? (Assume that
# the implicit stack space incurred due to recursion does not count).
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
