Add solution #128

Author: JoshCrozier

README.md

@@ -54,6 +54,7 @@
 118|[Pascal's Triangle](./0118-pascals-triangle.js)|Easy|
 119|[Pascal's Triangle II](./0119-pascals-triangle-ii.js)|Easy|
 121|[Best Time to Buy and Sell Stock](./0121-best-time-to-buy-and-sell-stock.js)|Easy|
+128|[Longest Consecutive Sequence](./0128-longest-consecutive-sequence.js)|Medium|
 133|[Clone Graph](./0133-clone-graph.js)|Medium|
 136|[Single Number](./0136-single-number.js)|Easy|
 141|[Linked List Cycle](./0141-linked-list-cycle.js)|Easy|

solutions/0128-longest-consecutive-sequence.js

@@ -0,0 +1,31 @@
+/**
+ * 128. Longest Consecutive Sequence
+ * https://leetcode.com/problems/longest-consecutive-sequence/
+ * Difficulty: Medium
+ *
+ * Given an unsorted array of integers nums, return the length of the
+ * longest consecutive elements sequence.
+ *
+ * You must write an algorithm that runs in O(n) time.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var longestConsecutive = function(nums) {
+  const set = new Set(nums);
+  let result = 0;
+
+  for (let i = 0; i < nums.length; i++) {
+    if (!set.has(nums[i] - 1)) {
+      let streak = 1;
+      while (set.has(nums[i] + streak)) {
+        streak++;
+      }
+      result = Math.max(result, streak);
+    }
+  }
+
+  return result;
+};