Feature/sherlock and anagrams

docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/sherlock_and_anagrams.md

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+# [Sherlock and Anagrams](https://www.hackerrank.com/challenges/sherlock-and-anagrams)
+
+- Difficulty:  `#medium`
+- Category: `#ProblemSolvingMedium` `#DictionariesAndHashmaps` `#Strings`
+
+Two strings are [http://en.wikipedia.org/wiki/Anagram](anagrams) of each other
+if the letters of one string can be rearranged to form the other string.
+Given a string, find the number of pairs of substrings of the string that are
+anagrams of each other.
+
+## Example
+
+`s = mom`
+
+The list of all anagrammatic pairs is `[m, m]`, `[mo, om]`
+at positions `[[0], [2]]`, `[[0, 1], [1, 2]]` respectively.
+
+## Function Description
+
+Complete the function sherlockAndAnagrams in the editor below.
+
+*sherlockAndAnagrams* has the following parameter(s):
+
+- `string s`: a string
+
+## Returns
+
+- `int`: the number of unordered anagrammatic pairs of substrings in **`s`**
+
+## Input Format
+
+The first line contains an integer `q`, the number of queries.
+Each of the next `q` lines contains a string `s` to analyze.
+
+## Constraints
+
+- $ 1 \leq 10 \leq 10 $
+- $ 2 \leq $ lenght of `s` $ \leq 100 $
+
+`s` contains only lowercase letters in the range ascii[a-z].
+
+## Sample Input 0
+
+```text
+2
+abba
+abcd
+```
+
+## Sample Output 0
+
+```text
+4
+0
+```
+
+## Explanation 0
+
+The list of all anagrammatic pairs is `[a, a]`, `[ab, ba]`,
+`[b, b]` and `[abb, bba]` at positions `[[0], [3]]`, `[[0, 1]], [[2, 3]]`,
+`[[1], [2]]` and `[[0, 1, 2], [1, 2, 3]]` respectively.
+
+No anagrammatic pairs exist in the second query as no character repeats.
+
+## Sample Input 1
+
+```text
+2
+ifailuhkqq
+kkkk
+````
+
+## Sample Output 1
+
+```text
+3
+10
+```
+
+## Explanation 1
+
+For the first query, we have anagram pairs `[i, i]`, `[q, q]`
+and `[ifa, fai]` at positions `[[0], [3]]`, `[[8], [9]]`
+and `[[0, 1, 2], [1, 2, 3]]` respectively.
+
+For the second query:
+
+There are `6` anagrams of the form `[k, k]` at positions `[[0, 1]]`,
+ `[[0], [2]]`, `[[0], [3]]`, `[[1], [2]]`, `[[1], [3]]` and `[[2], [3]]`.
+
+There are 3 anagrams of the form `[kk, kk]` at positions `[[0, 1], [1, 2]]`,
+`[[0, 1], [2, 3]]` and `[[1, 2], [2, 3]]`.
+
+There is 1 anagram of the form `[kkk, kkk]` at position `[[0, 1, 2], [1, 2, 3]]`.
+
+## Sample Input 2
+
+```text
+1
+cdcd
+```
+
+## Sample Output 2
+
+```text
+5
+```
+
+## Explanation 2
+
+There are two anagrammatic pairs of length `1`: `[c, c]` and `[d, d]`.
+There are three anagrammatic pairs of length `2`:
+`[cd, dc]`, `[cd, cd]`, `[dc, cd]` at positions
+`[[0, 1] [1, 2]]`, `[[0, 1], [2, 3]]`, `[1, 2], [2, 3]` respectively.

src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/sherlock_and_anagrams.test.ts

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+import { describe, expect, it } from '@jest/globals';
+import { logger as console } from '../../../logger';
+
+import { sherlockAndAnagrams } from './sherlock_and_anagrams';
+
+const TEST_CASES = [
+  {
+    title: 'Sample Test Case 0',
+    tests: [
+      {
+        input: 'abba',
+        expected: 4
+      },
+      {
+        input: 'abcd',
+        expected: 0
+      }
+    ]
+  },
+  {
+    title: 'Sample Test Case 1',
+    tests: [
+      {
+        input: 'ifailuhkqq',
+        expected: 3
+      },
+      {
+        input: 'kkkk',
+        expected: 10
+      }
+    ]
+  },
+  {
+    title: 'Sample Test Case 1',
+    tests: [
+      {
+        input: 'cdcd',
+        expected: 5
+      }
+    ]
+  }
+];
+
+describe('sherlock_and_anagrams', () => {
+  it('sherlockAndAnagrams test cases', () => {
+    expect.assertions(5);
+
+    TEST_CASES.forEach((testSet) => {
+      testSet.tests.forEach((test) => {
+        const answer = sherlockAndAnagrams(test.input);
+
+        console.debug(`checkMagazine(${test.input}) solution found: ${answer}`);
+
+        expect(answer).toStrictEqual(test.expected);
+      });
+    });
+  });
+});

src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/sherlock_and_anagrams.ts

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+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/sherlock_and_anagrams.md]]
+ */
+
+function factorial(n: number): number {
+  if (n == 0) {
+    return 1;
+  }
+  return n * factorial(n - 1);
+}
+
+export function sherlockAndAnagrams(s: string): number {
+  const candidates: Record<string, string[]> = {};
+  const size = s.length;
+
+  for (let i = 0; i < size; i++) {
+    for (let j = 0; j < size - i; j++) {
+      const substr = s.substring(i, size - j);
+
+      // Add substrings to a candidate list.
+      // two strings are anagrams if sorted strings are the same.
+
+      const anagram_candidate = substr
+        .split('')
+        .sort((a: string, b: string) => a.localeCompare(b))
+        .join('');
+      if (anagram_candidate in candidates) {
+        candidates[anagram_candidate].push(substr);
+      } else {
+        candidates[anagram_candidate] = [substr];
+      }
+    }
+  }
+
+  let count = 0;
+  // Final Anagram list
+  for (const i of Object.keys(candidates)) {
+    const total = candidates[i].length;
+    const k = 2;
+
+    if (total <= 1) {
+      delete candidates[i];
+    } else {
+      // Binomial coefficient: https://en.wikipedia.org/wiki/Binomial_coefficient
+      count += Math.floor(
+        factorial(total) / (factorial(k) * factorial(total - k))
+      );
+    }
+  }
+  console.debug(`filtered candidates: ${count}`);
+
+  return count;
+}
+
+export default { sherlockAndAnagrams };