How many digits appear in all integers from 0 to 100?
Integers where 9 will appear in 0-100 are: 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 , There are a total of 20 9s. A simple logarithmic analysis shows that the numbers can be divided into two categories:
- Take the remainder with 10 to get 9: 9, 19, 29, 39, 49, 59, 69, 79, 89, 99.
- Divide 10 to get 9: 90, 91, 92, 93, 94, 95, 96, 97, 98, 99. So we only need to record the number of occurrences of the two types of numbers.
- Below is the code implementation
#include<stdio.h>
int main()
{
int i=0;
int n = 0,m=0;
while (i <= 100)
{
if (i % 10 == 9)
{
++m;
}
if (i / 10 == 9)
{
++n;
}
++i;
}
printf("%d\n", m + n);
return 0;
}