leetcode-go/leetcode/easy/389.find-the-difference.go

func findTheDifference(s string, t string) byte {
	cnt := make([]int, 256)
	for _, r := range s {
		cnt[r]++
	}
	for _, r := range t {
		cnt[r]--
		if cnt[r] < 0 {
			return byte(r)
		}
	}
	return '0'
}