PAT甲级1049

1049. Counting Ones (30)

时间限制

10 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

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 (<=2³⁰).

Output Specification:

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

Sample Input:

12

Sample Output:

5

#include<cstdio>
int main()
{
  int n, a = 1, ans = 0;
  int left, now, right;
  scanf("%d", &n);
  while (n / a != 0)
  {
    left = n / (a * 10);
    now = n / a % 10;
    right = n%a;
    if (now == 0) ans += left*a;
    else if (now == 1)ans += left*a + right + 1;
    else ans += (left + 1)*a;
    a *= 10;
  }//从右至左，逐位分析“1”在该位出现的次数
  printf("%d\n", ans);
  return 0;
}