Find Number of Nodes in a Range in Python

Suppose we have a BST, and we also have left and right bounds l and r, we have to find the count of all nodes in root whose values are present in between l and r (inclusive).

So, if the input is like

l = 7, r = 13, then the output will be 3, as there are three nodes: 8, 10, 12.

To solve this, we will follow these steps−

• stack := a stack and insert root at first, count := 0

• while stack is not empty, do

  • node := top element of stack, and pop element

  • if node is not null, then

    • if l <= data of node <= r, then

      • count := count + 1

      • stack := push right of node and left of node into stack

    • otherwise when data of node < l, then

      • stack := push right of node into stack

      • otherwise,

      • stack := push left of node into stack

• return count

Example

 Live Demo

from collections import deque
class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.data = data
      self.left = left
      self.right = right
class Solution:
   def solve(self, root, l, r):
      stack, count = [root], 0
      while stack:
         node = stack.pop()
         if node:
            if l <= node.data <= r:
               count += 1
               stack += [node.right, node.left]
            elif node.data < l:
               stack += [node.right]
            else: stack += [node.left]
      return count
ob = Solution()
root = TreeNode(12)
root.left = TreeNode(8)
root.right = TreeNode(15)
root.left.left = TreeNode(3)
root.left.right = TreeNode(10)
print(ob.solve(root, 7,13))

Input

root = TreeNode(12)
root.left = TreeNode(8)
root.right = TreeNode(15)
root.left.left = TreeNode(3)
root.left.right = TreeNode(10)
7,13

Output

3