# [Leet Code] Find Largest Value in Each Tree Row

`Input: root = [1,3,2,5,3,null,9]Output: [1,3,9]`
`Input: root = [1,2,3]Output: [1,3]`
`Input: root = [1]Output: [1]`
`Input: root = [1,null,2]Output: [1,2]`
`Input: root = []Output: []`
`# Definition for a binary tree node.# class TreeNode(object):#     def __init__(self, val=0, left=None, right=None):#         self.val = val#         self.left = left#         self.right = rightclass Solution(object):    def largestValues(self, root):        """        :type root: TreeNode        :rtype: List[int]        """        if root:            elements = [[root.val]]            stack = [root]            self.helper(stack, elements)            for i in range(len(elements)):                elements[i] = max(elements[i])                            return elements        else:            return root                def helper(self, stack, elements):        while len(stack) > 0:            values = []            length = len(stack)            for i in range(length):                node = stack.pop(0)                if node.left:                    stack.append(node.left)                    values.append(node.left.val)                if node.right:                    stack.append(node.right)                    values.append(node.right.val)            if values != []:                elements.append(values)`

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