[小Trick]哈希值结构体

struct hashv {
    int len;
    ull val;
    hashv(char c) {
        val = c, len = 1;
    }
    hashv() : len(0), val(0) {}
    hashv operator+(hashv b)const {
        hashv ret;
        ret.len = len + b.len;
        ret.val = val + cf[len]*b.val;
        return ret;
    }
    bool operator==(hashv b)const {
        return len == b.len && val == b.val;
    }
};