Add solution #1530

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,349 LeetCode solutions in JavaScript
+# 1,350 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1169,6 +1169,7 @@
 1526|[Minimum Number of Increments on Subarrays to Form a Target Array](./solutions/1526-minimum-number-of-increments-on-subarrays-to-form-a-target-array.js)|Hard|
 1528|[Shuffle String](./solutions/1528-shuffle-string.js)|Easy|
 1529|[Minimum Suffix Flips](./solutions/1529-minimum-suffix-flips.js)|Medium|
+1530|[Number of Good Leaf Nodes Pairs](./solutions/1530-number-of-good-leaf-nodes-pairs.js)|Medium|
 1534|[Count Good Triplets](./solutions/1534-count-good-triplets.js)|Easy|
 1535|[Find the Winner of an Array Game](./solutions/1535-find-the-winner-of-an-array-game.js)|Medium|
 1550|[Three Consecutive Odds](./solutions/1550-three-consecutive-odds.js)|Easy|

solutions/1530-number-of-good-leaf-nodes-pairs.js

@@ -0,0 +1,51 @@
+/**
+ * 1530. Number of Good Leaf Nodes Pairs
+ * https://leetcode.com/problems/number-of-good-leaf-nodes-pairs/
+ * Difficulty: Medium
+ *
+ * You are 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.
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} distance
+ * @return {number}
+ */
+var countPairs = function(root, distance) {
+  let result = 0;
+  traverseTree(root);
+  return result;
+
+  function traverseTree(node) {
+    if (!node) return [];
+    if (!node.left && !node.right) return [1];
+
+    const leftDistances = traverseTree(node.left);
+    const rightDistances = traverseTree(node.right);
+
+    for (const left of leftDistances) {
+      for (const right of rightDistances) {
+        if (left + right <= distance) result++;
+      }
+    }
+
+    const allDistances = [];
+    for (const dist of leftDistances.concat(rightDistances)) {
+      if (dist + 1 <= distance) allDistances.push(dist + 1);
+    }
+
+    return allDistances;
+  }
+};