UVA 11038 How Many O's?——整数区间分解

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
typedef long long ll;
ll solve (ll num) {
if (num < 0) return 0;
ll ans = 1, left = num, right = 0, x = 1;
while (left >= 10) {
ll t = left % 10;
left /= 10;
if (t) ans += left*x;
else ans += (left-1)*x+(right+1);
right = right+t*x;
x *= 10;
}
return ans;
}
int main () {
ll n, m;
while (~scanf("%lld%lld", &n, &m) && n != -1 && m != -1) {
printf("%lld\n", solve(m) - solve(n-1));
}
return 0;
}