🚦 added challenge 9

Author: jamerrq

.gitignore

@@ -1 +1,3 @@
 node_modules/
+
+tricks.md

src/challenges/09.ts

@@ -0,0 +1,14 @@
+export function adjustLights (lights: string[]): number {
+  let o1 = 0
+  let o2 = 0
+  let index = 0
+  for (const light of lights) {
+    o1 += +(light !== '🟢') * +(index % 2 !== 0)
+    o2 += +(light !== '🔴') * +(index % 2 !== 0)
+    o1 += +(light !== '🔴') * +(index % 2 !== 1)
+    o2 += +(light !== '🟢') * +(index % 2 !== 1)
+    index++
+  }
+  const x = o1 - o2
+  return (x + 2 * o2 - ((x + (x >> 31)) ^ (x >> 31))) / 2
+}

src/tests/09.spec.ts

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+import { test, expectTypeOf, expect, describe } from 'vitest'
+import { adjustLights } from '../challenges/09'
+
+describe('Challenge #09', () => {
+  test('Test #01', () => {
+    expectTypeOf(adjustLights).returns.toEqualTypeOf(1)
+  })
+
+  // Test: adjustLights(["🟢", "🔴", "🟢", "🟢", "🟢"]) -> 1
+  test('Test #02', () => {
+    expect(adjustLights(['🟢', '🔴', '🟢', '🟢', '🟢'])).toEqual(1)
+  })
+
+  // Test: adjustLights(["🔴", "🔴", "🟢", "🟢", "🔴"]) -> 2
+  test('Test #03', () => {
+    expect(adjustLights(['🔴', '🔴', '🟢', '🟢', '🔴'])).toEqual(2)
+  })
+
+  // Test: adjustLights(["🟢", "🔴", "🟢", "🔴", "🟢"]) -> 0
+  test('Test #04', () => {
+    expect(adjustLights(['🟢', '🔴', '🟢', '🔴', '🟢'])).toEqual(0)
+  })
+
+  // Test: adjustLights(["🔴", "🔴", "🔴"] -> 1
+  test('Test #05', () => {
+    expect(adjustLights(['🔴', '🔴', '🔴'])).toEqual(1)
+  })
+})