codewars/go/kyu6/counting_duplicates/k.go

package kata

import "unicode"

func duplicate_count(s1 string) int {
	hits := make(map[rune]int)
	for _, r := range s1 {
		l := unicode.ToLower(r)
		n, _ := hits[l]
		hits[l] = n + 1
	}
	count := 0
	for _, n := range hits {
		if n > 1 {
			count++
		}
	}
	return count
}