题目：

题解：

func findLongestWord(s string, dictionary []string) (ans string) {
    m := len(s)
    f := make([][26]int, m+1)
    for i := range f[m] {
        f[m][i] = m
    }
    for i := m - 1; i >= 0; i-- {
        f[i] = f[i+1]
        f[i][s[i]-'a'] = i
    }

outer:
    for _, t := range dictionary {
        j := 0
        for _, ch := range t {
            if f[j][ch-'a'] == m {
                continue outer
            }
            j = f[j][ch-'a'] + 1
        }
        if len(t) > len(ans) || len(t) == len(ans) && t < ans {
            ans = t
        }
    }
    return
}