type strslice []string

func (ss strslice) Len() int { return len(ss) }
func (ss strslice) Less(i, j int) bool {
	if m, n := len(ss[i]), len(ss[j]); m != n {
		return n < m
	}
	return ss[i] < ss[j]
}
func (ss strslice) Swap(i, j int) { ss[i], ss[j] = ss[j], ss[i] }

func findLongestWord(s string, d []string) string {
	sort.Sort(strslice(d))
	for i := range d {
		if isSubstr(s, d[i]) {
			return d[i]
		}
	}
	return ""
}

func isSubstr(s, t string) bool {
	i, j, m, n := 0, 0, len(s), len(t)
	if m < n {
		return false
	}
	s1, s2 := []rune(s), []rune(t)
	for ; i < m && j < n; j++ {
		for ; i < m && s1[i] != s2[j]; i++ {
		}
		i++
	}
	return i <= m && j == n
}