[Hacker Rank] Interview Preparation Kit: String Manipulation: Alternating Characters. Solved ✅.

Author: Gonzalo Diaz

docs/hackerrank/interview_preparation_kit/string_manipulation/alternating-characters.md

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+# [Strings: Alternating Characters](https://www.hackerrank.com/challenges/alternating-characters)
+
+- Difficulty:  `#easy`
+- Category: `#ProblemSolvingBasic` `#strings`
+
+You are given a string containing characters `A` and `B` only.
+Your task is to change it into a string such that there are
+no matching adjacent characters.
+To do this, you are allowed to delete zero or more
+characters in the string.
+
+Your task is to find the minimum number of required deletions.
+
+## Example
+
+`s = AABAAB`
+
+Remove an at `A` positions `0` and `3` to make `s = ABAB` in `2` deletions.
+
+## Function Description
+
+Complete the alternatingCharacters function in the editor below.
+alternatingCharacters has the following parameter(s):
+
+- `string s`: a string
+
+## Returns
+
+- `int`: the minimum number of deletions required
+
+## Input Format
+
+The first line contains an integer `q`, the number of queries.
+The next `q` lines each contain a string `s` to analyze.
+
+## Constraints
+
+- $ 1 \leq q \leq 10 $
+- $ 1 \leq lenght of  s \leq 10^5 $
+- Each string `s` will consist only of characters `A` and `B`.
+
+## Sample Input
+
+```text
+5
+AAAA
+BBBBB
+ABABABAB
+BABABA
+AAABBB
+```
+
+## Sample Output
+
+```text
+3
+4
+0
+0
+4
+```
+
+## Explanation
+
+The characters marked red are the ones that can be deleted
+so that the string does not have matching adjacent characters.
+
+```text
+AAAA => A, 3 deletions
+BBBBB => B, 4 deletions
+ABABABAB => ABABABAB, 0 deletions
+BABABA => BABABA, 0 deletions
+AAABBB => AB, 4 deletions
+```

src/hackerrank/interview_preparation_kit/string_manipulation/alternating_characters.test.ts

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+import { describe, expect, it } from '@jest/globals';
+
+import { alternatingCharacters } from './alternating_characters';
+import TEST_CASES from './alternating_characters.testcases.json';
+
+describe('alternatingCharacters', () => {
+  it('alternatingCharacters test cases', () => {
+    expect.assertions(9);
+
+    TEST_CASES.forEach((testSet) => {
+      testSet?.tests.forEach((test) => {
+        const result = alternatingCharacters(test.input);
+
+        expect(result).toStrictEqual(test.expected);
+      });
+    });
+  });
+});

src/hackerrank/interview_preparation_kit/string_manipulation/alternating_characters.testcases.json

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+[
+  {
+    "title": "Sample Test case 0",
+    "tests": [
+      {
+        "input": "AAAA",
+        "expected": 3
+      },
+      {
+        "input": "BBBBB",
+        "expected": 4
+      },
+      {
+        "input": "ABABABAB",
+        "expected": 0
+      },
+      {
+        "input": "BABABA",
+        "expected": 0
+      },
+      {
+        "input": "AAABBB",
+        "expected": 4
+      }
+    ]
+  },
+  {
+    "title": "Sample Test case 13",
+    "tests": [
+      {
+        "input": "AAABBBAABB",
+        "expected": 6
+      },
+      {
+        "input": "AABBAABB",
+        "expected": 4
+      },
+      {
+        "input": "ABABABAA",
+        "expected": 1
+      }
+    ]
+  },
+  {
+    "title": "Sample Test case 14",
+    "tests": [
+      {
+        "input": "ABBABBAA",
+        "expected": 3
+      }
+    ]
+  }
+]

src/hackerrank/interview_preparation_kit/string_manipulation/alternating_characters.ts

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+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/string_manipulation/alternating-characters.md]]
+ */
+
+export function alternatingCharacters(s: string): number {
+  let last = '';
+  let newString = '';
+
+  for (const letter of s) {
+    if (letter !== last) {
+      newString += letter;
+
+      last = letter;
+    }
+  }
+
+  return s.length - newString.length;
+}
+
+export default { alternatingCharacters };