add kata

5kyu/buddy-pairs/solution.ts

@@ -0,0 +1,33 @@
+
+const properDivisors = (n: number): number[] => {
+  const divs: number[] = [];
+  for (let i = 1; i <= Math.sqrt(n); i++) {
+    if (n % i === 0) {
+      divs.push(i);
+      const otherDivisor = n / i;
+      if (otherDivisor !== i && otherDivisor !== n) {
+        divs.push(otherDivisor);
+      }
+    }
+  }
+
+  return divs;
+}
+
+const sumOfDivisors = (n: number): number => {
+  const divs = properDivisors(n)
+  return divs.reduce((acc, div) => acc + div, 0);
+}
+
+export function buddy(start: number, limit: number): number[] {
+  for (let n = start; n <= limit; n++) {
+    const sumN = sumOfDivisors(n);
+    const m = sumN - 1;
+    const sumM = sumOfDivisors(m);
+    if (m > n && sumM === n + 1) {
+      return [n, m];
+    }
+  }
+
+  return [];
+}