UVA 11038 - How Many O's?（计数问题）

#include <stdio.h>
#include <string.h>

long long a, b;

long long solve(long long left) {
	if (left < 0) return 0;
	long long ans = 1, mid, right = 0, j = 1;
	while (left >= 10) {
		mid = left % 10; left /= 10;
		if (mid) ans += left * j;
		else ans += (left - 1) * j + right + 1;
		right = right + mid * j;
		j *= 10;
  	}
  	return ans;
}

int main() {
	while (~scanf("%lld%lld", &a, &b) && a != -1 || b != -1) {
		printf("%lld\n", solve(b) - solve(a - 1));
 	}
	return 0;
}