Sum of squares in an array using recursion in golang - arrays

Question

So my friend gave me this task where the sum of squares of positive numbers must be calculated using recursion.
Conditions - The input will be a string with space separated numbers
This is what I've come so far but this shows a runtime error.
Here is the full error https://ideone.com/53oOjN
package main
import(
'fmt',
'strings',
'strconv'
)
var n int = 4
var sum_of_squares int = 0
func sumOfSquares(strArray []string, iterate int) int{
number, _ := strconv.Atoi(strArray[iterate])
if number > 0 {
sum_of_squares += number*number
}
if iterate == n {
return 0 // just to end the recursion
}
return sumOfSquares(strArray, iterate+1)
}
func main() {
str := "1 2 3 4"
strArray := strings.Fields(str)
result := sumOfSquares(strArray, 0)
fmt.Println(sum_of_squares, result)
}

Answer 1

The rule of thumb in recursion is termination condition. It should exist and it should exist in the right place.
func sumOfSquares(strArray []string, iterate int) int{
if iterate >= len(strArray) {
return sum_of_squares
}
number, _ := strconv.Atoi(strArray[iterate]) //TODO: handle err here
sum_of_squares += number*number
return sumOfSquares(strArray, iterate+1)
}
Just for you information: canonical recursion should not save it's state into global fields. I would suggest using following function signature.
func sumOfSquares(strArray []string, iterate, currentSum int) int{
//...
return sumOfSquares(strArray, iterate+1, sum_of_squares)
}
So that you don't need to store sum_of_squares somewhere. You will just pass it to next function invocation.

Answer 2

package main
import (
"fmt"
"strconv"
"strings"
)
var n int
func sumOfSquares(strArray []string, iterate int) int {
number, _ := strconv.Atoi(strArray[iterate])
if iterate == n {
return number * number
}
return ((number * number) + sumOfSquares(strArray, iterate+1))
}
func main() {
str := "1 2 3 4"
strArray := strings.Fields(str)
n = len(strArray) - 1
result := sumOfSquares(strArray, 0)
fmt.Println(result)
}
Indexing starts from 0, so decrease the length by one.
As #peterSO have pointed out, if strings contain unusual characters, it doesn't work, I didn't post the right answer for getting input because you seem to be beginner, but you can read the input, like this instead.
var inp []byte
var loc int
inp, _ = ioutil.ReadFile(fileName)
//add \n so that we don't end up running out of bounds,
//if last byte is integer.
inp = append(inp, '\n')
func scanInt() (res int) {
if loc < len(inp) {
for ; inp[loc] < 48 || inp[loc] > 57; loc++ {
}
for ; inp[loc] > 47 && inp[loc] < 58; loc++ {
res = res<<3 + res<<1 + (int(inp[loc]) - 48)
}
}
return
}
This is faster and scans integers only, and skips all other unusual characters.

Answer 3

I like to keep it simple. I have some few if conditions as well, but hope you like it.
func sumOfSquares(numArr []string) int {
i, err := strconv.Atoi(numArr[0])
rest := numArr[1:]
//Error checking
if err != nil {
fmt.Println(err)
os.Exit(1)
return 0
}
square := i * i
// negative & last number
if i < 0 && len(rest) == 0 {
return square
}
// negative & not last number
if i < 0 && len(rest) > 0 {
return sumOfSquares(rest)
}
// last man standing
if i >= 0 && len(rest) == 0 {
return square
}
return square + sumOfSquares(rest)
}
DEMO : https://play.golang.org/p/WWYxKbvzanJ