PROGRAMMERES Level 1 연습문제 시저 암호 (JAVA 자바)

import java.util.*;

class Solution {
    public String solution(String s, int n) {
        String answer = "";

        for(int i=0; i<s.length(); i++){
            // 대문자
            if((int)s.charAt(i) >= 65 && (int)s.charAt(i) <= 90){
                // Z를 넘어갈 경우
                if((int)s.charAt(i) + n > 90) {                    
                    int a = ((int)s.charAt(i) + n) - 90 + 64;
                    char ch = (char)a;
                    answer+= ch; 
                } else {
                    int a = (int)s.charAt(i) + n;
                    char ch = (char)a;
                    answer+= ch;
                }
            } 
            
            // 소문자
            else if((int)s.charAt(i) >= 97 && (int)s.charAt(i) <= 122){
                // z를 넘어갈 경우
                if((int)s.charAt(i) + n > 122) {
                    int a = ((int)s.charAt(i) + n) - 122 + 96;
                    char ch = (char)a;
                    answer+= ch;
                } else{
                    int a = (int)s.charAt(i) + n;
                    char ch = (char)a;
                    answer+= ch;
                }
            }
            
            // 공백
            else if(s.charAt(i)==' ') {
                answer+= s.charAt(i);                
            }
            
        }
        
        return answer;
    }
}