662. Maximum Width of Binary Tree

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When find result in one of tree level. Can use bfs.

# 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
class Solution:
    def widthOfBinaryTree(self, root: Optional[TreeNode]) -> int:

        dq = deque([[root, 0]])

        res = 0

        while dq:

            lens = len(dq)

            l, r = 0 , 0
            for i in range(lens):
                node, idx = dq.popleft()
                if i == 0:
                    l = idx
                if i == lens -1:
                    r = idx

                if node.left:
                    dq.append([node.left, 2*idx + 1])
                if node.right:
                    dq.append([node.right, 2*idx + 2])

                
            res = max(res, r - l + 1)

        return res