LeetCode: 543. Diameter of Binary Tree

题目

原题地址：https://leetcode.com/problems/diameter-of-binary-tree/

Given the root of a binary tree, return the length of the diameter of the tree.

The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

The length of a path between two nodes is represented by the number of edges between them.

Example 1:

image

Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3is the length of the path [4,2,1,3] or [5,2,1,3].

Example 2:

Input: root = [1,2]
Output: 1

Constraints:

  • The number of nodes in the tree is in the range [1, 10^4].
  • -100 <= Node.val <= 100

题目大意是，求二叉树的直径，直径的定义为任意两个节点间的最长路径

解法

左子数和右子树的最大深度之和即为二叉树的直径。

这个思路的 Python 代码类似下面这样：

# 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 diameterOfBinaryTree(self, root):
        self._max_path = 0

        self._max_deepth(root)

        return self._max_path

    def _max_deepth(self, root):
        if root is None:
            return 0

        left_deepth = self._max_deepth(root.left)
        right_deepth = self._max_deepth(root.right)

        path = left_deepth + right_deepth
        if path > self._max_path:
            self._max_path = path

        return 1 + max(left_deepth, right_deepth)

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