Syntax error Convert Sorted Array to Binary Search Tree in Python

Convert Sorted Array to Binary Search Tree in Python

Suppose we have one sorted array A. We have to generate one height-balanced binary search. In this problem, a height-balanced binary tree is actually a binary tree in which the depth of the two subtrees of every node never differs by more than 1. Suppose the array is like [-10, -3, 0, 5, 9]. So one possible output will be like: [0, -3, 9, -10, null, 5]

To solve this, we will follow these steps.

  • If A is empty, then return Null
  • find the mid element, and make it root
  • Divide the array into two sub-arrays, left part of the mid element, and right part of the mid element
  • recursively perform the same task for the left subarray and right subarray.

Let us see the following implementation to get a better understanding −

Example

 Live Demo

class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.data = data
      self.left = left
      self.right = right
def insert(temp,data):
   que = []
   que.append(temp)
   while (len(que)):
      temp = que[0]
      que.pop(0)
      if (not temp.left):
         if data is not None:
            temp.left = TreeNode(data)
         else:
            temp.left = TreeNode(0)
         break
      else:
         que.append(temp.left)
      if (not temp.right):
         if data is not None:
            temp.right = TreeNode(data)
      else:
         temp.right = TreeNode(0)
      break
   else:
      que.append(temp.right)
def make_tree(elements):
   Tree = TreeNode(elements[0])
   for element in elements[1:]:
      insert(Tree, element)
   return Tree
def height(root):
   if root is None:
      return 0
   else :
      # Compute the height of left and right subtree
      l_height = height(root.left)
      r_height = height(root.right)
      #Find the greater one, and return it
      if l_height > r_height :
         return l_height+1
      else:
         return r_height+1
def print_given_level(root, level):
   if root is None:
      return
   if level == 1:
      print(root.data,end = ',')
   elif level > 1 :
      print_given_level(root.left , level-1)
      print_given_level(root.right , level-1)
def level_order(root):
   print('[', end = '')
   h = height(root)
   for i in range(1, h+1):
      print_given_level(root, i)
   print(']')
class Solution(object):
   def sortedArrayToBST(self, nums):
      """
      :type nums: List[int]
      :rtype: TreeNode
      """
      if not nums:
         return None
      mid = nums[len(nums)//2]
      root = TreeNode(mid)
      root.left = self.sortedArrayToBST(nums[:len(nums)//2])
      root.right = self.sortedArrayToBST(nums[len(nums)//2 +1 :])
      return root
nums = [-10,-3,0,5,9]
ob1 = Solution()
bst = ob1.sortedArrayToBST(nums)
level_order(bst)

Input

nums = [-10,-3,0,5,9]

Output

[0,-3,9,-10,5,]
Updated on: 2020-04-28T09:18:12+05:30

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