Add week 4 solutions: longest-consecutive-sequence

Author: gitsunmin

longest-consecutive-sequence/gitsunmin.ts

@@ -0,0 +1,29 @@
+/**
+ * https://leetcode.com/problems/longest-consecutive-sequence
+ * time complexity : O(n)
+ * space complexity : O(n)
+ */
+const findStreak = (set: Set<number>) => (num: number): number => {
+    if (!set.has(num - 1)) return takeWhile(num, currentNum => set.has(currentNum)).length;
+    return 0;
+};
+
+const takeWhile = (start: number, predicate: (value: number) => boolean): number[] => {
+    const result: number[] = [];
+    let currentNum = start;
+    while (predicate(currentNum)) {
+        result.push(currentNum);
+        currentNum += 1;
+    }
+    return result;
+}
+
+const max = (maxStreak: number, currentStreak: number): number => Math.max(maxStreak, currentStreak);
+
+function longestConsecutive(nums: number[]): number {
+    const numSet = new Set(nums);
+
+    return [...numSet]
+        .map(findStreak(numSet))
+        .reduce(max, 0);
+}