✨ Challenge #11: The Studious Elves

Author: monicatvera

Diff for: 2023/challenge-11/README.md

@@ -0,0 +1,40 @@
+## Challenge #11: 📖 The Studious Elves
+
+In Santa's workshop, the elves are known for their love of puzzles and brain teasers. This year, they've come up with a special challenge: to create a Christmas palindrome.
+
+A palindrome is a word that reads the same forwards and backward. The task is to determine if it's possible to transform a given string into a palindrome with, at most, a single exchange of letters.
+
+```javascript
+/**
+ * Determines if it's possible to form a palindrome with at most one letter exchange.
+ * @param {string} word - The input string.
+ * @returns {(number[]|null)} - Returns an array of two indices if a palindrome can be formed with one change,
+ * an empty array if the input is already a palindrome, or null if it's not possible.
+ */
+function getIndexsForPalindrome(word) {
+  // Implementation goes here
+}
+```
+
+### Examples
+
+```javascript
+getIndexsForPalindrome('anna');      // Returns: []
+getIndexsForPalindrome('abab');      // Returns: [0, 1]
+getIndexsForPalindrome('abac');      // Returns: null
+getIndexsForPalindrome('aaaaaaaa');  // Returns: []
+getIndexsForPalindrome('aaababa');   // Returns: [1, 3]
+getIndexsForPalindrome('caababa');   // Returns: null
+```
+
+### Explanation
+
+- If the input string is already a palindrome, the function returns an empty array.
+- If it's not possible to form a palindrome, the function returns null.
+- If a palindrome can be formed with one change, the function returns an array with the two positions (indexes) that must be swapped to create it.
+
+**Note:**
+
+- The function should always return the first valid pair of indices if multiple swaps are possible.
+- Ensure the provided examples match the expected output.
+- Feel free to add more examples or edge cases to thoroughly test the function.

Diff for: 2023/challenge-11/solution.js

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+function getIndexsForPalindrome(word) {
+  const isPalindrome = (str) => str === str.split("").reverse().join("");
+
+  if (isPalindrome(word)) {
+    return [];
+  }
+
+  for (let i = 0; i < word.length; i++) {
+    for (let j = i + 1; j < word.length; j++) {
+      const swapped = [...word];
+      [swapped[i], swapped[j]] = [swapped[j], swapped[i]];
+      if (isPalindrome(swapped.join(""))) {
+        return [i, j];
+      }
+    }
+  }
+
+  return null;
+}

Diff for: 2023/challenge-11/solution.spec.js

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+import { getIndexsForPalindrome } from "./solution";
+
+describe("Challenge #11: 📖 The Studious Elves", () => {
+  const testCases = [
+    createTestCase(
+      ["anna"],
+      [],
+      "should return an empty array for an input that is already a palindrome"
+    ),
+    createTestCase(
+      ["abab"],
+      [0, 1],
+      "should return the indices for a single swap palindrome"
+    ),
+    createTestCase(
+      ["abac"],
+      null,
+      "should return null for an input where no palindrome can be formed"
+    ),
+    createTestCase(
+      ["aaaaaaaa"],
+      [],
+      "should return an empty array for a string of the same characters"
+    ),
+    createTestCase(
+      ["aaababa"],
+      [1, 3],
+      "should return the indices for a single swap palindrome"
+    ),
+    createTestCase(
+      ["caababa"],
+      null,
+      "should return null for an input where no palindrome can be formed"
+    ),
+  ];
+
+  it.each(testCases)("#$# $description", ({ input, expected, description }) => {
+    expect(getIndexsForPalindrome(...input)).toEqual(expected);
+  });
+});
+
+function createTestCase(input, expected, description) {
+  return { input, expected, description };
+}

Diff for: README.md

@@ -107,6 +107,7 @@ This repository contains the solutions to the challenges proposed by [@midudev](
 | 08  |        [Sorting the warehouse](2023/challenge-08)         |       🟠       | [Show](2023/challenge-08/solution.js) |
 | 09  |        [Switch the lights](2023/challenge-09)         |       🟢       | [Show](2023/challenge-09/solution.js) |
 | 10  |        [Create your own Christmas tree](2023/challenge-10)         |       🟢       | [Show](2023/challenge-10/solution.js) |
+| 11  |        [Challenge #11: 📖 The studious elves](2023/challenge-11)         |       🟠       | [Show](2023/challenge-11/solution.js) |
 
 [^1]: **Difficulty**: 🟢 Easy 🟠 Medium 🔴 Hard 🟣 Very Hard