<找工作 三>统计1到N中1出现的个数

#include <iostream>
using namespace std;
unsigned long long countOneNum(unsigned long long   N);
int main(){
	unsigned long long n=123;
	cout<<"-----------Start Count N:"<<n<<" One Numbers------------"<<endl;
	unsigned long long result=countOneNum(n);
	cout<<"-----------One Numbers: "<<result<<"------------"<<endl;
	getchar();
}
unsigned long long countOneNum(unsigned long long   n){
	unsigned long long highNum=1;
	unsigned long long midNum=0;
	unsigned long long lowNum=0;
	unsigned long long count=0;
	unsigned long long factor=1;
	while(highNum>0){
		highNum=n/(factor*10);		
		lowNum=n%factor;
		midNum=n/factor%10;
		switch (midNum){
		case 0:
			count+=highNum*factor;
			break;
		case 1:
			count+=highNum*factor+lowNum+1;
			break;
		default:
			count+=(highNum+1)*factor;

		}
		factor*=10;
	}
	return count;
}

 很有意思的东西