hdu3709

枚举+数位dp

注意处理数字为0和1的情况。

#include <cstdio>

#include <cstring>

using namespace std;



#define D(x) 



const int MAX_DIGIT = 20;



long long n;

int f[MAX_DIGIT];

long long memoize[MAX_DIGIT][20*20*9];

int pivot;



int to_digits(long long a)

{

    int ret = 0;

    while (a > 0)

    {

        f[++ret] = a % 10;

        a /= 10;

    }

    return ret;

}



long long dfs(int digit, bool less, int weight)

{

    if (digit <= 0)

    {

        return weight == 0;

    }

    if (less && memoize[digit][weight] != -1)

    {

        return memoize[digit][weight];

    }

    int limit = less ? 9 : f[digit];

    long long ret = 0;

    for (int i = 0; i <= limit; i++)

    {

        int new_weight = weight + (digit - pivot) * i;

        if (new_weight < 0)

        {

            continue;

        }

        ret += dfs(digit - 1, less || i < f[digit], new_weight);

    }

    memoize[digit][weight] = ret;

    return ret;

}



long long work(long long n)

{

    if (n < 0)

    {

        return 0;

    }

    int len = to_digits(n);

    long long ret = 0;

    for (int i = 1; i <= len; i++)

    {

        pivot = i;

        memset(memoize, -1, sizeof(memoize));

        ret += dfs(len, false, 0);

    }

    return ret - len + 1;

}



int main()

{

    int t;

    scanf("%d", &t);

    while (t--)

    {

        long long a, b;

        scanf("%lld%lld", &a, &b);

        printf("%lld\n", work(b) - work(a - 1));

    }

    return 0;

}

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