Google Interview Questions - Aarray Multiplicator

main.go

package main

import "fmt"

/**
* There is an array A[N] of N numbers.
* You have to compose an array Output[N] such that Output[i]
* will be equal to multiplication of all the elements of A[N] except A[i].
* For example Output[0] will be multiplication of A[1] to A[N-1]
* and Output[1] will be multiplication of A[0] and from A[2] to A[N-1].
* Solve it without division operator and in O(n).
 */

func Multiply(arr []int) []int {
	output := make([]int, 0)

	if len(arr) == 0 {
		return output
	}

	output = append(output, 0)
	for i := range arr {
		if i == 0 {
			continue
		}

		if i == 1 {
			output = append(output, arr[0])
			continue
		}

		previousIndex := i - 1

		sum := arr[previousIndex] * output[previousIndex]

		output = append(output, sum)
	}

	return output
}

func main() {

	primes := []int{1, 2, 3, 4, 5, 6}
	fmt.Printf("%v\n", primes)

	fmt.Printf("%v\n", Multiply(primes))
}

main_test.go

package main

import (
	"testing"
)

func TestMe(t *testing.T) {
	input := []int{1, 2, 3, 4, 5, 6}
	expected := []int{0, 1, 2, 6, 24, 120}

	got := Multiply(input)

	for i, n := range got {
		if expected[i] != n {
			t.Errorf("Wrong!\nwant: %v\ngot: %v\n", expected, got)
			t.Fail()
		}
	}
}

func TestOneItem(t *testing.T) {
	input := []int{1}
	expected := []int{0}

	got := Multiply(input)

	for i, n := range got {
		if expected[i] != n {
			t.Errorf("Wrong!\nwant: %v\ngot: %v\n", expected, got)
			t.Fail()
		}
	}
}

func TestEmpty(t *testing.T) {
	input := []int{}
	expected := []int{}

	got := Multiply(input)

	for i, n := range got {
		if expected[i] != n {
			t.Errorf("Wrong!\nwant: %v\ngot: %v\n", expected, got)
			t.Fail()
		}
	}
}