func firstUniqChar(s string) int {
res := 1<<63 - 1
for c := 'a'; c <= 'z'; c ++ {
left := strings.Index(s, string(c))
right := strings.LastIndex(s, string(c))
if left >= 0 && left == right {
if res > left {
res = left
}
}
}
if res == 1<<63-1 {
return -1
}
return res
}