max_nonrepeat_string.go

package main

import (
	"fmt"
)

func main() {
	fmt.Println(find("abcabcd"))
}

func find(src string) string {
	lastChar := make(map[rune]int)
	var maxLength, start int

	runes := []rune(src)
	for charIndex, char := range runes {
		if last, ok := lastChar[char]; ok && last >= start {
			start = last + 1
		}
		if length := charIndex - start + 1; length > maxLength {
			maxLength = length
		}
		lastChar[char] = charIndex
	}
	return string(runes[start : start+maxLength])
}