Add solution #454

Author: JoshCrozier

0454-4sum-ii.js

@@ -0,0 +1,27 @@
+/**
+ * 454. 4Sum II
+ * https://leetcode.com/problems/4sum-ii/
+ * Difficulty: Medium
+ *
+ * Given four integer arrays nums1, nums2, nums3, and nums4 all of length n, return the number
+ * of tuples (i, j, k, l) such that:
+ * - 0 <= i, j, k, l < n
+ * - nums1[i] + nums2[j] + nums3[k] + nums4[l] == 0
+ */
+
+/**
+ * @param {number[]} nums1
+ * @param {number[]} nums2
+ * @param {number[]} nums3
+ * @param {number[]} nums4
+ * @return {number}
+ */
+var fourSumCount = function(nums1, nums2, nums3, nums4) {
+  const map = new Map();
+  nums1.forEach(n1 => {
+    nums2.forEach(n2 => map.set(n1 + n2, (map.get(n1 + n2) || 0) + 1));
+  });
+  return nums3.reduce((count, n3) => {
+    return count + nums4.reduce((sum, n4) => sum + (map.get(-(n3 + n4)) || 0), 0);
+  }, 0);
+};

README.md

@@ -307,6 +307,7 @@
 450|[Delete Node in a BST](./0450-delete-node-in-a-bst.js)|Medium|
 451|[Sort Characters By Frequency](./0451-sort-characters-by-frequency.js)|Medium|
 452|[Minimum Number of Arrows to Burst Balloons](./0452-minimum-number-of-arrows-to-burst-balloons.js)|Medium|
+454|[4Sum II](./0454-4sum-ii.js)|Medium|
 456|[132 Pattern](./0456-132-pattern.js)|Medium|
 459|[Repeated Substring Pattern](./0459-repeated-substring-pattern.js)|Easy|
 461|[Hamming Distance](./0461-hamming-distance.js)|Easy|