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Rooted by: Multiples of 3 or 5
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  • Code 
    package kata

func IntegerSum(n int) (sum int) {
  sum = n * (n+1) / 2
  return
}

func AddMultiples(n int) (sum int) {
  sum = IntegerSum((n-1)/3) * 3 + IntegerSum((n-1)/5) * 5 - IntegerSum((n-1)/15) * 15
  return 
}
     Test Cases 
    package kata_test
import (
  . "github.com/onsi/ginkgo"
  . "github.com/onsi/gomega"
  . "codewarrior/kata"
)
var _ = Describe("Multiples of 3 and 5", func() {
   
   It("should handle basic cases", func() {
     Expect(AddMultiples(10)).To(Equal(23))
     Expect(AddMultiples(20)).To(Equal(78))
   })
   
   It("should handle zeroes", func() {
     Expect(AddMultiples(0)).To(Equal(0))
     Expect(AddMultiples(1)).To(Equal(0))
   })
   
   It("should handle large numbers", func() {
     Expect(AddMultiples(200)).To(Equal(9168))
   })
})
    View Run Output
  • Code
    • package kata
    • func AddMultiples(n int) (sum int) {
    • for i := 1; i < n; i++ {
    • if i % 3 == 0 || i % 5 == 0 {
    • sum += i
    • }
    • }
    • func IntegerSum(n int) (sum int) {
    • sum = n * (n+1) / 2
    • return
    • }
    • func AddMultiples(n int) (sum int) {
    • sum = IntegerSum((n-1)/3) * 3 + IntegerSum((n-1)/5) * 5 - IntegerSum((n-1)/15) * 15
    • return
    • }