longest consecutive seq solution

Author: nancyel

longest-consecutive-sequence/nancyel.ts

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+/**
+ * requirement: return result in linear time (O(n))
+ */
+function longestConsecutive(nums: number[]): number {
+  if (nums.length === 0) return 0;
+
+  const numSet = new Set(nums); // O(1) lookups
+  let maxLength = 0;
+
+  for (const num of numSet) {
+    // key: determine the "start" of a consecutive sequence.
+    // approach: if num - 1 doesn't exist in the set → num is the start of a sequence.
+    if (!numSet.has(num - 1)) {
+      let currentNum = num;
+      let currentLength = 1;
+
+      // count consecutive numbers
+      while (numSet.has(currentNum + 1)) {
+        currentNum++;
+        currentLength++;
+      }
+
+      maxLength = Math.max(maxLength, currentLength);
+    }
+  }
+  return maxLength;
+}