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543. Diameter of Binary Tree ​

题目 ​

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:

Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is 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, 104].
  • -100 <= Node.val <= 100
Related Topics
  • 树
  • 深度优先搜索
  • 二叉树

  • 👍 1758
  • 👎 0

    • 思路 ​

    记录最大直径，需要使用一个全局变量来 track 每次找到的最大值

    否则记录的是最后找到的一条直径长度

    解法 ​

    py
    # leetcode submit region begin(Prohibit modification and deletion)
# 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: Optional[TreeNode]) -> int:
        if not root:
            return 0

        self.res = 0

        def dfs(root: Optional[TreeNode]) -> int:
            if not root:
                return 0

            left = dfs(root.left)

            right = dfs(root.right)

            self.res = max(left + right, self.res)

            return max(right, left) + 1
        dfs(root)
        return self.res
        
# leetcode submit region end(Prohibit modification and deletion)

    复杂度分析 ​

    • 时间复杂度 O(N)
    • 空间复杂度 O(H)