Syntax error Program to convert level order binary tree traversal to linked list in Python

Program to convert level order binary tree traversal to linked list in Python

Suppose we have a binary search tree, we have to convert it to a singly linked list using levelorder traversal.

So, if the input is like

then the output will be [5, 4, 10, 2, 7, 15, ]

To solve this, we will follow these steps −

  • head := a new linked list node

  • currNode := head

  • q := a list with value root

  • while q is not empty, do

    • curr := delete first element from q

    • if curr is not null, then

      • next of currNode := a new linked list node with value of curr

      • currNode := next of currNode

      • insert left of curr at the end of q

      • insert right curr at the end of q

  • return next of head

Let us see the following implementation to get better understanding −

Example

class ListNode:
   def __init__(self, data, next = None):
      self.val = data
      self.next = next
class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.val = data
      self.left = left
      self.right = right

def print_list(head):
   ptr = head
   print('[', end = "")
   while ptr:
      print(ptr.val, end = ", ")
      ptr = ptr.next
print(']')
   
class Solution:
   def solve(self, root):
      head = ListNode(None)
      currNode = head
      q = [root]
      while q:
         curr = q.pop(0)
         if curr:
            currNode.next = ListNode(curr.val)
            currNode = currNode.next
            q.append(curr.left)
            q.append(curr.right)
      return head.next

ob = Solution()
root = TreeNode(5)
root.left = TreeNode(4)
root.right = TreeNode(10)
root.left.left = TreeNode(2)
root.right.left = TreeNode(7)
root.right.right = TreeNode(15)
head = ob.solve(root)
print_list(head)

Input

root = TreeNode(5)
root.left = TreeNode(4)
root.right = TreeNode(10)
root.left.left = TreeNode(2)
root.right.left = TreeNode(7)
root.right.right = TreeNode(15)
head = ob.solve(root)

Output

[5, 4, 10, 2, 7, 15, ]
Updated on: 2020-10-10T11:02:09+05:30

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