LeetCode #872 Leaf-Similar Trees

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Problem

Consider all the leaves of a binary tree. From left to right order, the values of those leaves form a leaf value sequence.

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For example, in the given tree above, the leaf value sequence is (6, 7, 4, 9, 8).

Two binary trees are considered leaf-similar if their leaf value sequence is the same.

Return true if and only if the two given trees with head nodes root1 and root2 are leaf-similar.

Note:

  • Both of the given trees will have between 1 and 100 nodes.

Solution

Method: Depth-First Search (Preorder Traversal)

Time Complexity: O(T1 + T2)

Space Complexity: O(T1 + T2)

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

class Solution:
    def leafSimilar(self, root1, root2):
        """
        :type root1: TreeNode
        :type root2: TreeNode
        :rtype: bool
        """
        def leaves(root):
            ret = []
            stack = [root]
            while stack:
                node = stack.pop()
                if node:
                    stack.append(node.right)
                    stack.append(node.left)
                    if node.left is None and node.right is None:
                        ret.append(node.val)
            return ret
        
        return leaves(root1) == leaves(root2)