LeetCode: 872. Leaf-Similar Trees

题目

原题地址:https://leetcode.com/problems/leaf-similar-trees/

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

image1

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.

Example 1:

image2

Input: root1 = [3,5,1,6,2,9,8,null,null,7,4], root2 = [3,5,1,6,7,4,2,null,null,null,null,null,null,9,8]
Output: true

Example 2:

Input: root1 = [1], root2 = [1]
Output: true

Example 3:

Input: root1 = [1], root2 = [2]
Output: false

Example 4:

Input: root1 = [1,2], root2 = [2,2]
Output: true

Example 5:

image5

Input: root1 = [1,2,3], root2 = [1,3,2]
Output: false

Constraints:

  • The number of nodes in each tree will be in the range [1, 200].
  • Both of the given trees will have values in the range [0, 200].

解法

遍历二叉树(比如前序遍历之类的))找到 root1 和 root2 的 leaf value sequence ,然后比较两个列表内的值是否相等。

这个方法的 Python 代码类似下面这样:

# 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 = right
class Solution(object):
    def leafSimilar(self, root1, root2):
        leafs_1 = self.collect_leafs(root1, [])
        leafs_2 = self.collect_leafs(root2, [])
        return leafs_1 == leafs_2

    def collect_leafs(self, root, values):
        if root is None:
            return values

        if root.left is None and root.right is None:
            values.append(root.val)

        self.collect_leafs(root.left, values)
        self.collect_leafs(root.right, values)

        return values

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