牛客网：字符串变形

import java.util.*;

public class Solution {
    public String trans(String s, int n) {
        // write code here
       StringBuffer sb = new StringBuffer();
        int left = s.length() - 1;
        while (left >= 0){
            String str = "";
            while (left >= 0  && s.charAt(left) != ' '){
                str += s.charAt(left);
                left--;
            }
            sb.append(reverse(str) + " ");
            left--;
        }
        sb.delete(sb.length() - 1, sb.length());
        return sb.toString();
    }

    private String reverse(String s){
        String res = "";
        for (int i = s.length() - 1; i >= 0; i--){
            if (s.charAt(i) >= 'A' && s.charAt(i) <= 'Z'){
                res += (char)(s.charAt(i) - 'A' + 'a');
            } else {
                res += (char)(s.charAt(i) - 'a' + 'A');
            }
        }
        return res;
    }
}