3. Digit Counts

淩亂°似流年 2022-05-27 03:43 223阅读 0赞

3. Digit Counts

Description

Count the number of k's between 0 and n. k can be 0 - 9.

Example

if n = 12, k = 1 in
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
we have FIVE 1's (1, 10, 11, 12)

Solution

import java.util.ArrayList;
public class Solution { 
    /* * @param : An integer * @param : An integer * @return: An integer denote the count of digit k in 1..n */
    public int digitCounts(int k, int n) {
        // write your code here
        if(n==0 && k==0) return 1;
        ArrayList<Integer> bits = new ArrayList<>();
        int nn = n;
        int sum = 0;
        while(nn>0){
            bits.add(nn%10);
            nn /= 10;
        }
        nn = 1;
        for(int i=0;i<bits.size();i++){
            nn *= 10;
            if(i>0 && i==bits.size()-1 && k==0){
                break;
            }
            if(k > bits.get(i)) sum = sum + n / nn * (nn / 10);
            else if(k==bits.get(i)) {
                if(i==0){
                    sum = sum + n / nn * (nn / 10) + 1;
                }else{
                    sum = sum + n / nn * (nn / 10) + 1 + n % (nn/10);
                }
            }else{
                sum = sum + (n / nn + 1) * (nn / 10);
            }
        }
        return sum;
    }
};