Solve 'Find the smallest' kata

Author: borisskert

src/find-the-smallest/smallest.ts

@@ -0,0 +1,58 @@
+/**
+ * https://www.codewars.com/kata/573992c724fc289553000e95/train/typescript
+ */
+export function smallest (n: number): number[] {
+  return Result.potentialResults(n)
+    .reduce(Result.min)
+    .toArray()
+}
+
+class Result {
+  private constructor (
+    private readonly value: number,
+    private readonly i: number,
+    private readonly j: number
+  ) {}
+
+  toArray (): number[] {
+    return [this.value, this.i, this.j]
+  }
+
+  static potentialResults (n: number): Result[] {
+    const size = n.toString().length
+
+    return cartesianProduct(size)
+      .map(({ i, j }) => {
+        const value = moveDigit(n, i, j)
+        return new Result(value, i, j)
+      })
+  }
+
+  static min (a: Result, b: Result): Result {
+    return a.value <= b.value ? a : b
+  }
+}
+
+function cartesianProduct (a: number, b: number = a): Array<{ i: number, j: number }> {
+  return intRange(0, a)
+    .flatMap(i =>
+      intRange(0, b)
+        .map(j => ({ i, j }))
+    )
+}
+
+function intRange (start: number, end: number): number[] {
+  const n = end - start + 1
+
+  return Array.from(Array(n).keys())
+    .map(x => x + start)
+}
+
+function moveDigit (n: number, i: number, j: number): number {
+  const digits = n.toString().split('')
+
+  const digit = digits.splice(i, 1)[0]
+  digits.splice(j, 0, digit)
+
+  return Number(digits.join(''))
+}

test/find-the-smallest/smallest.spec.ts

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+import { smallest } from '../../src/find-the-smallest/smallest'
+import chai, { assert } from 'chai'
+
+chai.config.truncateThreshold = 0
+
+describe('Fixed Tests smallest', function () {
+  it('Basic tests', function () {
+    assert.deepEqual(smallest(261235), [126235, 2, 0])
+    assert.deepEqual(smallest(209917), [29917, 0, 1])
+    assert.deepEqual(smallest(285365), [238565, 3, 1])
+    assert.deepEqual(smallest(269045), [26945, 3, 0])
+    assert.deepEqual(smallest(296837), [239687, 4, 1])
+  })
+})