UVa 11038 How many 0's.cpp

#include <cstdio>
#include <cmath>
using namespace std;
typedef long long int llt;

llt sum0 (llt n)
{
    llt N = n,sum = 0;
    int left=1,mid,right=1;
    while (N >= 10){
        mid = N%10;
        N /= 10;
        if (mid) sum += (N * left);
        else sum += ((N-1)*left + n%right +1);
        left *= 10;
        right *= 10;
    }
    return sum;
}
int main()
{
    llt m,n;
    while (scanf("%lld%lld",&m,&n)){
        if (m < 0) break;
        llt ans = sum0(n) - sum0(m-1);
        if (m == 0) ans++;    // 函數是從1~m，如果m==0會少算
        printf("%lld\n",ans);
    }
    return 0;
}