Added longest consecutive solution

Author: nhistory

longest-consecutive-sequence/nhistory.js

@@ -0,0 +1,30 @@
+var longestConsecutive = function (nums) {
+  // Return 0 if there are no elements in nums
+  if (nums.length === 0) return 0;
+
+  // Create a set to find values efficiently
+  const numSet = new Set(nums);
+  let maxLength = 0;
+
+  for (let num of numSet) {
+    // Check if this is the start of a sequence
+    if (!numSet.has(num - 1)) {
+      let currentNum = num;
+      let currentLength = 1;
+
+      // Count the length of the sequence
+      while (numSet.has(currentNum + 1)) {
+        currentNum += 1;
+        currentLength += 1;
+      }
+
+      // Update the maximum length
+      maxLength = Math.max(maxLength, currentLength);
+    }
+  }
+
+  return maxLength;
+};
+
+// TC: O(n)
+// SC: O(n)