LightOJ 1140 How Many Zeroes?

#include <cstdio>
#include <cstring>
#include <string>
#include <iostream>
#include <queue>
#include <stack>
#include <algorithm>
#include <map>
#include <vector>
#include <cmath>
#include <stack>
using namespace std;
#define ll long long
#define int64 __int64
#define M 50005
#define N 1005
#define inf 1000010
#define mod 1000000009

int dig[55];
ll dp[55][2] , table[55];

ll Dfs(int index , int fg , int lim)
{
if (!index)return !fg;
if (!lim && dp[index][fg] != -1)return dp[index][fg];
int i , up = lim ? dig[index] : 9;
ll ret = 0;
for (i = 0 ; i <= up ; i++)
{
if (fg && i == 0)
{
if (!(lim&&i==up))ret += table[index-1]+Dfs(index-1 , 1 , 0);
else
{
int j ;
ll temp = 0;
for (j = index-1 ; j > 0 ; j--)temp = temp*10+dig[j];
temp++;
ret += temp+Dfs(index-1 , 1 , 1);
}
}
else
ret += Dfs(index-1 , fg||i!=0 , lim&&i==up);
}
if (!lim)dp[index][fg] = ret;
return ret;
}

ll Solve(ll k)
{
if (k < 0)return 0;
int len = 0;
while (k)
{
dig[++len] = k%10;
k /= 10;
}
return Dfs(len , 0 , 1);
}

int main()
{
ll m , n;
int i , t , tcase = 1;
scanf("%d",&t);
memset(dp , -1 , sizeof dp);
table[0] = 1;
for (i = 1 ; i <= 25 ; i++)table[i] = table[i-1]*10;
while (t--)
{
scanf("%lld%lld",&m,&n);
printf("Case %d: %lld\n",tcase++,Solve(n)-Solve(m-1));
}
return 0;
}