102-BinaryTreeLevelOrderTraversal

Binary Tree Level Order Traversal

Problem can be found in here!

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

Solution: Breadth-First Search

class Solution:
    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
        if root is None:
            return []

        queue, output_list = collections.deque([root]), []
        while queue:
            level = []
            for _ in range(len(queue)):
                node = queue.popleft()
                level.append(node.val)
                if node.left is not None:
                    queue.append(node.left)
                if node.right is not None:
                    queue.append(node.right)
            output_list.append(level)

        return output_list

Explanation: We can solve this problem by using breadth-first search (BFS). To support performing BFS on the binary tree, we need to use a queue. As we iterate the whole binary tree, we will get the level-order traversal of given binary tree.

Time Complexity: , Space Complexity: