Merge pull request #206 from TheGeniusOfEternity/feature/interview/group-numbers

Feat | Interview | #15 Group Numbers

Author: TheGeniusOfEternity

README.md

@@ -133,4 +133,5 @@ Interview Questions
 - [Task #11](src/interview/build-tree/no-replies-sort) - _Build Tree: No Replies Sort_
 - [Task #12](src/interview/build-tree/with-replies-sort) - _Build Tree: With Replies Sort_
 - [Task #13](src/interview/build-comments-tree) - _Build Comments Tree_
-- [Task #13](src/interview/find-by-type) - _Find By Type_
+- [Task #13](src/interview/find-by-type) - _Find By Type_
+- [Task #14](src/interview/group-numbers) - _Group Numbers_

src/interview/group-numbers/solution.test.ts

@@ -0,0 +1,64 @@
+import { groupNumbers } from './solution';
+
+describe('Group Numbers | Interview | Testcases', () => {
+  test('#1 Groups numbers with same digit multiset (ignoring zeros)', () => {
+    const numbers = [123, 321, 1023, 3201, 112, 12];
+    const result = groupNumbers(numbers);
+    expect(result).toEqual([[123, 321, 1023, 3201], [112], [12]]);
+  });
+
+  test('#2 Handles empty array', () => {
+    expect(groupNumbers([])).toEqual([]);
+  });
+
+  test('#3 Single number – one group', () => {
+    expect(groupNumbers([42])).toEqual([[42]]);
+  });
+
+  test('#4 Numbers with zeros are grouped correctly', () => {
+    const numbers = [101, 110, 11, 1001];
+    // 101 → digits {1,1} (zeros ignored) → "11"
+    // 110 → digits {1,1} → "11"
+    // 11  → digits {1,1} → "11"
+    // 1001 → digits {1,1} → "11"
+    expect(groupNumbers(numbers)).toEqual([[101, 110, 11, 1001]]);
+  });
+
+  test('#5 Different digit counts -> different groups', () => {
+    const numbers = [12, 122, 112];
+    // 12 → "12"
+    // 122 → "122" (two 2s, one 1)
+    // 112 → "112" (two 1s, one 2)
+    expect(groupNumbers(numbers)).toEqual([[12], [122], [112]]);
+  });
+
+  test('#6 Preserves input order within groups', () => {
+    const numbers = [321, 123, 213, 321];
+    const result = groupNumbers(numbers);
+    expect(result).toEqual([[321, 123, 213, 321]]);
+  });
+
+  test('#7 Groups with same digits but different zeros', () => {
+    const numbers = [105, 501, 150, 51];
+    // 105 → "15"
+    // 501 → "15"
+    // 150 → "15"
+    // 51  → "15"
+    expect(groupNumbers(numbers)).toEqual([[105, 501, 150, 51]]);
+  });
+
+  test('#8 Groups appear in order of first occurrence', () => {
+    const numbers = [99, 123, 90009, 1032, 45, 54];
+    // 99 → "99"
+    // 123 → "123"
+    // 90009 → "99"
+    // 1032 → "123"
+    // 45 → "45"
+    // 54 → "45"
+    expect(groupNumbers(numbers)).toEqual([
+      [99, 90009],
+      [123, 1032],
+      [45, 54],
+    ]);
+  });
+});

src/interview/group-numbers/solution.ts

@@ -0,0 +1,49 @@
+/**
+ * Groups nums by multiset of digits (except zero)
+ * @param numbers - array of positive integers
+ * @returns array of groups
+ *
+ * @example
+ *
+ * 123   -> 123
+ * 1032  -> 123
+ * 99    -> 99
+ * 90009 -> 99
+ *
+ * const numbers = [99, 123, 90009, 1032, 45, 54];
+ * const snapshot = [...numbers];
+ *
+ * console.log(groupNumbersByDigits(numbers));
+ * // Expected:
+ * // [
+ * //   [99, 90009],
+ * //   [123, 1032],
+ * //   [45, 54]
+ * // ]
+ *
+ * console.log(numbers);
+ * Must be unchanged [99, 123, 90009, 1032, 45, 54]
+ */
+export const groupNumbers = (numbers: number[]): number[][] => {
+  const result: number[][] = [];
+  const groups = new Map<string, number[]>();
+  for (const num of numbers) {
+    const count = new Array<number>(10).fill(0);
+    for (const d of num.toString()) {
+      if (d !== '0') {
+        count[Number(d)]++;
+      }
+    }
+    const key = count.join(',');
+    if (!groups.has(key)) {
+      groups.set(key, []);
+    }
+    groups.get(key)?.push(num);
+  }
+
+  for (const [, group] of groups) {
+    result.push(group);
+  }
+
+  return result;
+};