Program to find number of only child in a binary tree in python

Suppose we have a binary tree; we have to find the number of nodes that are an only child. As we know a node x is called an only child node when its parent has exactly one child that is x.

So, if the input is like

then the output will be 2 as 8 and 6 are the only children.

To solve this, we will follow these steps:

• if root is null, then
  • return 0
• d := a double ended queue
• insert root at the end of d
• count := 0
• while d is not empty, do
  • current := left element of d and delete left element
  • if left of current is not null, then
    • insert left of current into d
    • if right of current is null, then
      • count := count + 1
    • if right of current is not null, then
      • insert right of current into d
      • if left of current is null, then
        • count := count + 1
• return count

Let us see the following implementation to get better understanding:

Example Code

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):       if not root:          return 0       d = deque()       d.append(root)       count = 0       while d:          current = d.popleft()          if current.left:             d.append(current.left)             if not current.right:                count += 1             if current.right:                d.append(current.right)                if not current.left:                   count += 1          return count ob = Solution() root = TreeNode(9) root.left = TreeNode(7) root.right = TreeNode(10) root.left.right = TreeNode(8) root.right.right = TreeNode(6) print(ob.solve(root))

Input

root = TreeNode(9) 
root.left = TreeNode(7)
root.right = TreeNode(10)
root.left.right = TreeNode(8)
root.right.right = TreeNode(6)

Output

2