1049. Counting Ones (30) [count 1] -- PAT (Advanced Level) Practise

1049. Counting Ones (30) [count 1] -- PAT (Advanced Level) Practise
Question Information

1049. Counting Ones (30)

Time limit 10 MS
The memory limit is 65536 kB.
Code length limit: 16000 B

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

Solutions

In the beauty of programming, the number of numbers ranging from 0 to N containing number 1 is calculated.

AC code

#include 
  
   int get(long long n){    long long cur = 0, before = 0, after = 0, i = 1, cnt = 0;    while ((n / i) != 0){        cur = n / i % 10;        before = n / i / 10;        after = n - (n / i) * i;        if (cur == 0){            cnt += before * i;        }else if (cur == 1){            cnt += before * i + after + 1;        }else {            cnt += (before + 1) * i;        }        i *= 10;    }    return cnt;}int main(){    long long a;    scanf("%lld", &a);    printf("%d\n", get(a));    return 0;}