LightOJ 1140 - How Many Zeroes? (数位dp)

#include <stdio.h>
#include <iostream>
#include <map>
#include <set>
#include <list>
#include <stack>
#include <vector>
#include <math.h>
#include <string.h>
#include <queue>
#include <string>
#include <stdlib.h>
#include <algorithm>
//#define LL __int64
#define LL long long
#define eps 1e-12
#define PI acos(-1.0)
using namespace std;
const int INF = 0x3f3f3f3f;
const int maxn = 4010;

LL dp[25][25];
int dig[25];

LL dfs(int len, int first, int sta, int up)
{
	if(len == 0)
	{
		if(first)
			return (LL)1;
		else
			return (LL)sta;
	}
	if(!up && dp[len][sta] != -1 && !first)
		return dp[len][sta];
	int n = up ? dig[len] : 9;
	LL res = 0;
	for(int i = 0; i <= n; i++)
	{
		if(first)
		{
			res += dfs(len-1,first&&i==0,0,up&&i==n);
		}
		else
		{
			if(i == 0)
				res += dfs(len-1,0,sta+1,up&&i==n);
			else
				res += dfs(len-1,0,sta,up&&i==n);
		}
	}
	if(!up && !first)
		dp[len][sta] = res;
	return res;
}

LL cal(LL num)
{
	int len = 0;

	if(num == 0)
		dig[++len] = 0;
	while(num)
	{
		dig[++len] = num % 10;
		num /= 10;
	}
	return dfs(len,1,0,1);
}

int main()
{
	int test;
	LL a,b;
	scanf("%d",&test);
	for(int item = 1; item <= test; item++)
	{
		scanf("%lld %lld",&a,&b);
		memset(dp,-1,sizeof(dp));
		printf("Case %d: %lld\n",item,cal(b) - cal(a-1) );
	}
	return 0;
}