func canConstruct(ransomNote string, magazine string) bool {
	m, n := len(ransomNote), len(magazine)
	if n < m {
		return false
	}
	cnt := make([]int, 256)
	for _, r := range magazine {
		cnt[r]++
	}
	for _, r := range ransomNote {
		cnt[r]--
		if cnt[r] < 0 {
			return false
		}
	}
	return true
}