Talk is cheap.
func longestSubstringWithoutDuplication(s string) int {
index, res, start, tmp := [128]int{}, 0, 0, 0
for i, j := range s {
if start < index[j] { start = index[j] }
tmp = i - start + 1
if res < tmp { res = tmp }
index[j] = i + 1
}
return res
}