Create 108-convert_sorted_arr_into_bst.py

Author: stevestar888

108-convert_sorted_arr_into_bst.py

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+"""
+https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/submissions/
+
+Strat: Look for the middle elem, then recurse on left and right.
+
+Stats:
+    Runtime: 72 ms, faster than 24.04% of Python online submissions for Convert Sorted Array to Binary Search Tree.
+    Memory Usage: 17 MB, less than 65.96% of Python online submissions for Convert Sorted Array to Binary Search Tree.
+
+"""
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def sortedArrayToBST(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: TreeNode
+        """
+        if nums:
+            mid = len(nums) // 2
+            return self.helper(nums[:mid], nums[mid], nums[mid + 1:])
+        else:
+            return None
+        
+    def helper(self, left, mid, right):
+        # print(left, mid, right)
+        parent = TreeNode(mid)
+        
+        #work out left node
+        if left:
+            mid = len(left) // 2
+            parent.left = self.helper(left[:mid], left[mid], left[mid + 1:])
+        
+        #work out right node
+        if right:
+            mid = len(right) // 2
+            parent.right = self.helper(right[:mid], right[mid], right[mid + 1:])
+        
+        return parent
+