Golang: find first character in a String that doesn't repeat - go

Question

I'm trying to write a function that returns the finds first character in a String that doesn't repeat, so far I have this:
package main
import (
"fmt"
"strings"
)
func check(s string) string {
ss := strings.Split(s, "")
smap := map[string]int{}
for i := 0; i < len(ss); i++ {
(smap[ss[i]])++
}
for k, v := range smap {
if v == 1 {
return k
}
}
return ""
}
func main() {
fmt.Println(check("nebuchadnezzer"))
}
Unfortunately in Go when you iterate a map there's no guarantee of the order so every time I run the code I get a different value, any pointers?

Answer 1

Using a map and 2 loops :
play
func check(s string) string {
m := make(map[rune]uint, len(s)) //preallocate the map size
for _, r := range s {
m[r]++
}
for _, r := range s {
if m[r] == 1 {
return string(r)
}
}
return ""
}
The benfit of this is using just 2 loops vs multiple loops if you're using strings.ContainsRune, strings.IndexRune (each function will have inner loops in them).

Answer 2

Efficient (in time and memory) algorithms for grabbing all or the first unique byte http://play.golang.org/p/ZGFepvEXFT:
func FirstUniqueByte(s string) (b byte, ok bool) {
occur := [256]byte{}
order := make([]byte, 0, 256)
for i := 0; i < len(s); i++ {
b = s[i]
switch occur[b] {
case 0:
occur[b] = 1
order = append(order, b)
case 1:
occur[b] = 2
}
}
for _, b = range order {
if occur[b] == 1 {
return b, true
}
}
return 0, false
}
As a bonus, the above function should never generate any garbage. Note that I changed your function signature to be a more idiomatic way to express what you're describing. If you need a func(string) string signature anyway, then the point is moot.

Answer 3

That can certainly be optimized, but one solution (which isn't using map) would be:
(playground example)
func check(s string) string {
unique := ""
for pos, c := range s {
if strings.ContainsRune(unique, c) {
unique = strings.Replace(unique, string(c), "", -1)
} else if strings.IndexRune(s, c) == pos {
unique = unique + string(c)
}
}
fmt.Println("All unique characters found: ", unique)
if len(unique) > 0 {
_, size := utf8.DecodeRuneInString(unique)
return unique[:size]
}
return ""
}
This is after the question "Find the first un-repeated character in a string"
krait suggested below that the function should:
return a string containing the first full rune, not just the first byte of the utf8 encoding of the first rune.