feat(solutions): add triangle-type/typescript/function

challenges/triangle-type/solutions/typescript/function/README.md

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+# triangle-type/typescript/function
+
+Created by [@Divlo](https://github.com/Divlo) on 30 June 2021.

challenges/triangle-type/solutions/typescript/function/solution.ts

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+import readline from 'readline'
+
+const removeByIndex = <T = any>(array: T[], index: number): T[] => {
+  const result = [...array]
+  result.splice(index, 1)
+  return result
+}
+
+type TriangleType = 'impossible' | 'equilateral' | 'isosceles' | 'scalene'
+
+class Triangle {
+  public sides: number[]
+  public type: TriangleType
+
+  constructor(sides: number[]) {
+    this.sides = sides
+    this.type = this.getType()
+  }
+
+  private getType(): TriangleType {
+    const largestSide = Math.max(...this.sides)
+    const largestSideIndex = this.sides.findIndex((side) => side === largestSide)
+    const otherSides = removeByIndex(this.sides, largestSideIndex)
+    const isImpossible = otherSides[0] + otherSides[1] < largestSide
+    if (isImpossible) {
+      return 'impossible'
+    }
+    const uniqueSides = [...new Set(this.sides)]
+    const isEquilateral = uniqueSides.length === 1
+    const isIsocseles = uniqueSides.length === 2
+    if (isEquilateral) {
+      return 'equilateral'
+    }
+    if (isIsocseles) {
+      return 'isosceles'
+    }
+    return 'scalene'
+  }
+}
+
+const triangleSides: number[] = []
+const readlineInterface = readline.createInterface({
+  input: process.stdin,
+  output: process.stdout
+})
+readlineInterface.on('line', (value) => {
+  triangleSides.push(Number(value))
+})
+readlineInterface.on('close', solution)
+
+function solution(): void {
+  const triangle = new Triangle(triangleSides)
+  console.log(triangle.type)
+}