Number of Digit One

Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.

For example:
Given n = 13,
Return 6, because digit 1 occurred in the following numbers: 1, 10, 11, 12, 13.

Hint:

1. Beware of overflow.

 1 int countDigitOne(int n) {

 2     int count=0;

 3     long m=1;

 4     for(m=1;m<=n;m=m*10)

 5     {

 6         count+=(n/m+8)/10*m;

 7         if(n/m%10==1)

 8           count+=n%m+1;

 9     }

10     return count;

11 }