func CheckPermutation(s1 string, s2 string) bool {
if len(s1) != len(s2) {
return false
}
cnt := make([]int, 26)
for _, c := range s1 {
cnt[c-'a']++
for _, c := range s2 {
if cnt[c-'a']--; cnt[c-'a'] < 0 {
return true