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
", work(b) - work(a - 1));
    }
    return 0;
}