501

Author: tech-cow

README.md

@@ -71,7 +71,7 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |110|[Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/#/description)| [Python [Yu]](./tree/Yu/110_isBalanced.py) | _O(N)_| _O(h)_  | Easy | ||
 |112|[Path Sum](https://leetcode.com/problems/path-sum/#/description)| [Python [Yu]](./tree/Yu/112_hasPathSum.py) | _O(N)_| _O(h)_  | Easy | |[中文讲解](https://www.youtube.com/watch?v=LgtcGjIuE18&feature=youtu.be)|
 |404|[Sum of Left Leaves](https://leetcode.com/problems/sum-of-left-leaves/#/description)| [Python [Yu]](./tree/Yu/404_sum_of_Left_Leaves.py) | _O(N)_| _O(h)_  | Easy | ||
-|543|[Diameter of Binary Tree](https://leetcode.com/problems/diameter-of-binary-tree/#/description)| [Python [Yu]](./tree/Yu/543.py) | _O(N)_| _O(h)_  | Easy | |[公瑾讲解](https://www.youtube.com/watch?v=0VnOfu2pYTo)|
+
 
 
 
@@ -90,6 +90,9 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |-----|-------| -------- | ---- | ------|------------|---|-----|
 |108|[Convert Sorted Array to Binary Search Tree](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/#/solutions)| [Python [Yu]](./tree/Yu/108.py) | _O(N)_| _O(N)_  | Easy | |[公瑾讲解](https://www.youtube.com/watch?v=lBrb4fXPcMM)|
 |226|[Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/#/description)| [Python [Yu]](./tree/Yu/226.py) | _O(N)_| _O(1)_  | Easy | |[公瑾讲解](https://youtu.be/oiX3mqcAK0s)|
+|543|[Diameter of Binary Tree](https://leetcode.com/problems/diameter-of-binary-tree/#/description)| [Python [Yu]](./tree/Yu/543.py) | _O(N)_| _O(h)_  | Easy | |[公瑾讲解](https://www.youtube.com/watch?v=0VnOfu2pYTo)|
+|501|[Find Mode in Binary Search Tree](https://leetcode.com/problems/find-mode-in-binary-search-tree/#/description)| [Python [Yu]](./tree/Yu/501.py) | _O(N)_| _O(N)_  | Easy | |[公瑾讲解](https://youtu.be/v4F4x_uwMb8)|
+
 |563|[Binary Tree Tilt](https://leetcode.com/problems/binary-tree-tilt/#/description)| [Python [Yu]](./tree/Yu/563.py) | _O(N)_| _O(1)_  | Easy | |[公瑾讲解](https://youtu.be/47FQVP4ynk0)|
 |257|[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/#/description)| [Python [Yu]](./tree/Yu/257.py) | _O(N)_| _O(N)_  | Easy | |[公瑾讲解](https://youtu.be/Zr_7qq2f16k)|
 |102|[Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/#/description)| [Python [Yu]](./tree/Yu/102.py) | _O(N)_| _O(N)_  | Medium | |[公瑾讲解](https://youtu.be/IWiprpdSgzg)|

tree/Yu/501.py

@@ -0,0 +1,47 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# Author: Yu Zhou
+# 501. Find Mode in Binary Search Tree
+# ****************
+# Descrption:
+# Given a binary search tree (BST) with duplicates, find all the mode(s)
+# (the most frequently occurred element) in the given BST.
+# ****************
+
+class Solution(object):
+    def findMode(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[int]
+        """
+
+        def find_hash(root, hash):
+            # Edge:
+            if not root:
+                return
+
+            # Process
+            if root.val in hash:
+                hash[root.val] += 1
+            else:
+                hash[root.val] = 1
+
+            # Recursion
+            find_hash(root.left, hash)
+            find_hash(root.right, hash)
+
+        # Edge
+        if not root:
+            return []
+
+        hash = {}
+        res = []
+        find_hash(root, hash)
+
+        max_value = max(hash.values())
+
+        for key in hash.keys():
+            if hash[key] == max_value:
+                res.append(key)
+        return res