面试题32 1的数目

<<剑指offer>>的解释没有编程之美的解释好。建议这题看编程之美的解释

long long CountOne(long long n)
{
	long long iCount = 0;
	
	long long ifactor = 1;
	
	long long ilower, icur, ihigher;
	
	while( n/ifactor != 0)
	{
		ilower = n % ifactor ;
		icur = (n/ifactor )%10 ;
		ihigher = n/(ifactor*10);
		
		switch(icur){
		
			case 0: iCount += ihigher * ifactor;break;
			
			case 1: iCount += ihigher * ifactor + ilower + 1; break;
			
			default : iCount += (ihigher +1) * ifactor; 
		}
		
		ifactor *= 10;
	}
	
	return iCount;
}