feat(2023): add solution for challenge #21

2023/challenge-21/README.md

@@ -0,0 +1,24 @@
+# Challenge #21: Binary message
+
+The elves are receiving strange binary messages from Mars 🪐. Are the aliens trying to communicate with them? 👽
+
+**The message that arrives is an array of 0s and 1s**. It seems they have found a pattern… To make sure, they want to **find the longest segment of the string where the number of 0s and 1s is equal.**
+
+```js
+findBalancedSegment([1, 1, 0, 1, 1, 0, 1, 1])
+//                         |________|
+// position of segment:    [2, 5]
+// longest balanced
+// of 0s and 1s
+
+findBalancedSegment([1, 1, 0])
+//                      |__|
+//                     [1, 2]
+
+findBalancedSegment([1, 1, 1])
+// no balanced segments: []
+```
+
+Keep in mind that if there is more than one balanced pattern, **you should return the longest and the first one you find from left to right.**
+
+They say that if they find the pattern, they will be able to send a message back to Mars 🚀. It seems that they have to send it to `https://mars.codes`.

2023/challenge-21/challenge-21.test.ts

@@ -0,0 +1,20 @@
+import { describe } from 'vitest'
+import { findBalancedSegment } from './challenge-21'
+
+const TEST_CASES: TestCases<number[], number[]> = [
+  { args: [1, 1, 0, 1, 1, 0, 1, 1], expected: [2, 5] },
+  { args: [1, 1, 0], expected: [1, 2] },
+  { args: [1, 1, 1], expected: [] },
+  { args: [1, 0, 1], expected: [0, 1] },
+  { args: [1, 0, 1, 0], expected: [0, 3] },
+  { args: [1, 1, 0, 1, 0, 1], expected: [1, 4] },
+  { args: [1, 0, 0, 0, 1, 1, 1, 0, 0, 0], expected: [0, 7] },
+  { args: [0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1], expected: [5, 10] },
+]
+
+describe('Challenge #21: Binary message', () => {
+  buildChallengeTestCases({
+    cases: TEST_CASES,
+    fn: findBalancedSegment,
+  })
+})

2023/challenge-21/challenge-21.ts

@@ -0,0 +1,27 @@
+export function findBalancedSegment(message: number[]) {
+  const segment = [0, 0]
+
+  for (const [i, binary] of message.entries()) {
+    let ones = binary
+    let zeros = +(binary === 0)
+    const currentSegment = [i, i]
+
+    for (const [j, number] of message.slice(i + 1).entries()) {
+      ones += number
+      zeros += +(number === 0)
+
+      if (ones === zeros) {
+        currentSegment[1] = j + i + 1
+      }
+    }
+
+    if (currentSegment[1] - currentSegment[0] > segment[1] - segment[0]) {
+      segment[0] = currentSegment[0]
+      segment[1] = currentSegment[1]
+    }
+  }
+
+  if (segment[1] === 0) return []
+
+  return segment
+}

README.md

@@ -109,7 +109,7 @@ This repository contains the solutions to the challenges proposed by [@midudev](
 | 18  |       The digital clock        |       🔴       | [Show](https://adventjs.dev/challenges/2023/18) | [Go](./2023/challenge-18/challenge-18.ts) |
 | 19  |       Face the sabotage        |       🟠       | [Show](https://adventjs.dev/challenges/2023/19) | [Go](./2023/challenge-19/challenge-19.ts) |
 | 20  |     Distribute the weight      |       🔴       | [Show](https://adventjs.dev/challenges/2023/20) | [Go](./2023/challenge-20/challenge-20.ts) |
-| 21  |               --               |       --       |                       --                        |                    --                     |
+| 21  |         Binary message         |       🟠       | [Show](https://adventjs.dev/challenges/2023/21) | [Go](./2023/challenge-21/challenge-21.ts) |
 | 22  |               --               |       --       |                       --                        |                    --                     |
 | 23  |               --               |       --       |                       --                        |                    --                     |
 | 24  |               --               |       --       |                       --                        |                    --                     |