1530. Number of Good Leaf Nodes Pairs
https://leetcode.com/problems/number-of-good-leaf-nodes-pairs
Description
Given the root
of a binary tree and an integer distance
. A pair of two different leaf nodes of a binary tree is said to be good if the length of the shortest path between them is less than or equal to distance
.
Return the number of good leaf node pairs in the tree.
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].
Example 4:
**Input:** root = [100], distance = 1
**Output:** 0
Example 5:
**Input:** root = [1,1,1], distance = 2
**Output:** 1
Constraints:
The number of nodes in the
tree
is in the range[1, 2^10].
Each node's value is between
[1, 100]
.1 <= distance <= 10
ac
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