longest-consecutive-sequence

Author: taewanseoul

longest-consecutive-sequence/taewanseoul.ts

@@ -0,0 +1,33 @@
+/**
+ * 128. Longest Consecutive Sequence
+ * 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.
+ * https://leetcode.com/problems/longest-consecutive-sequence/description/
+ */
+function longestConsecutive(nums: number[]): number {
+  const set = new Set(nums);
+  const sorted = [...set].sort((a, b) => a - b);
+
+  if (sorted.length === 0) {
+    return 0;
+  }
+
+  let longestSequence = 1;
+  let currentSequence = 1;
+  for (let i = 0; i - 1 < sorted.length; i++) {
+    if (Math.abs(sorted[i + 1] - sorted[i]) === 1) {
+      currentSequence++;
+    } else {
+      if (currentSequence > longestSequence) {
+        longestSequence = currentSequence;
+      }
+      currentSequence = 1;
+    }
+  }
+
+  return longestSequence;
+}
+
+// O(n) time
+// O(n) space