#1530

Number of Good Leaf Nodes Pairs

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Description

Given the root of a binary tree and an integer distance, two distinct leaf nodes form a good pair if the length of the shortest path connecting them is at most distance. Return the total count of good leaf-node pairs.

Example 1:

Input: root = [1,2,3,null,4], distance = 3

Output: 1

Explanation: The leaf nodes of the tree are 3 and 4 and the length of the shortest path between them is 3. This is the only good pair.

Example 2:

Input: root = [1,2,3,4,5,6,7], distance = 3

Output: 2

Explanation: The good pairs are [4,5] and [6,7] with shortest path = 2. The pair [4,6] is not good because the length of ther shortest path between them is 4.

Example 3:

Input: root = [7,1,4,6,null,5,3,null,null,null,null,null,2], distance = 3

Output: 1

Explanation: The only good pair is [2,5].

Code

# 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 countPairs(self, root: Optional[TreeNode], distance: int) -> int:

# 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 countPairs(self, root: Optional[TreeNode], distance: int) -> int: