Add solution #1995

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,676 LeetCode solutions in JavaScript
+# 1,677 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1530,6 +1530,7 @@
 1992|[Find All Groups of Farmland](./solutions/1992-find-all-groups-of-farmland.js)|Medium|
 1993|[Operations on Tree](./solutions/1993-operations-on-tree.js)|Medium|
 1994|[The Number of Good Subsets](./solutions/1994-the-number-of-good-subsets.js)|Hard|
+1995|[Count Special Quadruplets](./solutions/1995-count-special-quadruplets.js)|Easy|
 1996|[The Number of Weak Characters in the Game](./solutions/1996-the-number-of-weak-characters-in-the-game.js)|Medium|
 2000|[Reverse Prefix of Word](./solutions/2000-reverse-prefix-of-word.js)|Easy|
 2011|[Final Value of Variable After Performing Operations](./solutions/2011-final-value-of-variable-after-performing-operations.js)|Easy|

solutions/1995-count-special-quadruplets.js

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+/**
+ * 1995. Count Special Quadruplets
+ * https://leetcode.com/problems/count-special-quadruplets/
+ * Difficulty: Easy
+ *
+ * Given a 0-indexed integer array nums, return the number of distinct quadruplets
+ * (a, b, c, d) such that:
+ * - nums[a] + nums[b] + nums[c] == nums[d], and
+ * - a < b < c < d
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var countQuadruplets = function(nums) {
+  const map = new Map();
+  let result = 0;
+
+  for (let c = nums.length - 2; c >= 2; c--) {
+    map.set(nums[c + 1], (map.get(nums[c + 1]) || 0) + 1);
+    for (let a = 0; a < c - 1; a++) {
+      for (let b = a + 1; b < c; b++) {
+        const sum = nums[a] + nums[b] + nums[c];
+        result += map.get(sum) || 0;
+      }
+    }
+  }
+
+  return result;
+};