Given a binary search tree (BST) with duplicates, find all the mode(s) (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 / 2return [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).
思路：遍历二叉树，利用map存储每一个不同的值及其出现的次数，并且在遍历的过程中记录最大的出现次数。
转载于:https://www.cnblogs.com/vincent93/p/6686623.html
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