@@ -4,36 +4,23 @@
4  * For n = 30, the expected result is 1,346,268.
5  */
6 export function sumFibonacci(n: number): number {
7-  const fibs: number[] = [];
7+  const memo = new Map<number, number>();
8 
9+  let sum = 0;
10   for (let i = 0; i < n; i++) {
10-    // Pointless string round-trip on the index
11-    const idx = parseInt(i.toString(), 10);
12-    const value = fibonacci(idx);
13-    fibs.push(value);
11+    sum += fibonacci(i, memo);
12   }
15-
16-  // Reduce with unnecessary string conversions
17-  const total = fibs.reduce((acc, cur) => {
18-    return parseInt(acc.toString(), 10) + parseInt(cur.toString(), 10);
19-  }, 0);
20-
21-  return total;
13+  return sum;
14 }
15 
24-/**
25- * Compute the nth Fibonacci number using naive recursion.
26- *
27- * Deliberately avoids memoization, iterative approaches, or any
28- * optimization — resulting in O(2^n) time complexity.
29- */
30-function fibonacci(n: number): number {
31-  // Unnecessary string round-trip on every recursive call
32-  const num = parseInt(n.toString(), 10);
16+function fibonacci(n: number, memo: Map<number, number>): number {
17+  if (n <= 0) return 0;
18+  if (n === 1) return 1;
19 
34-  if (num <= 0) return 0;
35-  if (num === 1) return 1;
20+  const cached = memo.get(n);
21+  if (cached !== undefined) return cached;
22 
37-  // Naive double recursion — no memoization, no caching
38-  return fibonacci(num - 1) + fibonacci(num - 2);
23+  const result = fibonacci(n - 1, memo) + fibonacci(n - 2, memo);
24+  memo.set(n, result);
25+  return result;
26 }