[프로그래머스/자바] k의 개수

class Solution {
    public int solution(int i, int j, int k) {
        int answer = 0;
        
        StringBuilder sb = new StringBuilder();
        
        for (int a = i; a <= j; a++) {
            sb.append(a + "");
        }
        
        String s = sb.toString();
        
        return s.length() - s.replace(Integer.toString(k), "").length();
    }
}