Populating Next Right Pointers in Each Node

Tree BFS

Problem

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition:

struct Node {
  int val;
  Node *left;
  Node *right;
  Node *next;
}

Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.

Initially, all next pointers are set to NULL.

Thought Process

• While traversing a level we will remember the previous node to connect it with the current node

Solution

from collections import deque
class Solution:
    def connect(self, root: 'Node') -> 'Node':
        if root is None:
            return
        
        queue = deque()
        queue.append(root)
        while queue:
            previousNode = None
            levelSize = len(queue)
            
            for _ in range(levelSize):
                currentNode = queue.popleft()
                if previousNode:
                    previousNode.next = currentNode
                previousNode = currentNode
                
                if currentNode.left:
                    queue.append(currentNode.left)
                if currentNode.right:
                    queue.append(currentNode.right)
        return root

#Time: O(n)
#Space: O(n) b/c of queue