lintcode-medium-Digit Counts

class Solution {
    /*
     * param k : As description.
     * param n : As description.
     * return: An integer denote the count of digit k in 1..n
     */
    public int digitCounts(int k, int n) {
        // write your code here
        
        int count = 0;
        
        for(int i = k ; i <= n; i++){
            count += singleCount(i, k);
        }
        
        return count;
    }
    
    public int singleCount(int num, int k){
        if(num == 0 && k == 0)
            return 1;
        
        int count = 0;
        
        while(num > 0){
            if(num % 10 == k)
                count++;
            
            num /= 10;
        }
        
        return count;
    }
    
};