1049. Counting Ones (30)

#include <iostream>using namespace std;int main()
{int n;scanf("%d", &n);int low, mid, high, d = 1, res = 0;while(n >= d){high = n / (d * 10);mid = (n - high * d * 10) / d;low = n % d;if(mid == 0){res += high * d;}else if(mid == 1){res += high * d + low + 1;}else{res += (high + 1) * d;}d *= 10;}printf("%d\n", res);system("pause");return 0;
}