1049 Counting Ones （30 分） 数学规律题

1049 Counting Ones （30 分）

The task is simple: given any positive integer N, you are supposed to count the total number of 1's in the decimal form of the integers from 1 to N. For example, given N being 12, there are five 1's in 1, 10, 11, and 12.

Input Specification:

Each input file contains one test case which gives the positive N (≤2​30​​).

Output Specification:

For each test case, print the number of 1's in one line.

Sample Input:

12

Sample Output:

5

比如21910

//21910
//(1 * 10000) + (2 * 1000 + 910 + 1 ) + (22 * 100) + ( 219 * 10 + 1) +(2191)

#include
using namespace std;
int main()
{
	int sum = 0, n , a = 1;
	scanf("%d", &n);
	int kk;
	while(n / a != 0)
	{
		int left = n / (a * 10);
		int now = n / a % 10;
		int right = n % a;
		kk = sum;
		if(now == 0)
			sum += left * a;
		else if(now == 1)
			sum += left * a + right + 1;
		else 
			sum +=(left + 1) * a; 	
		a = a * 10;
		printf("%d  \n", sum - kk);
	} 
	cout<