题解 | #字符串变形#

import java.util.*;

public class Solution {
    public String trans(String s, int n) {
        // write code here
        if(n==0){
            return s;
        }
        StringBuffer res = new StringBuffer();
        for(int i = 0;i<n;i++){
            if(Character.isLowerCase(s.charAt(i))){
                res.append(Character.toUpperCase(s.charAt(i)));
            }else if(Character.isUpperCase(s.charAt(i))){
                res.append(Character.toLowerCase(s.charAt(i)));
            }else{
                res.append(s.charAt(i));
            }
        }
        Stack<String> stack = new Stack<>();
        for(int i = 0;i<n;i++){
            int j = i;
            while(j<n&&res.charAt(j) != ' '){
                j++;
            }
            stack.push(res.substring(i,j));
            i=j;
        }
        if(s.charAt(n-1) == ' '){
            res = new StringBuffer(" ");
        }else{
            res = new StringBuffer();
        }
        while(!stack.isEmpty()){
            res.append(stack.pop());
            if(!stack.isEmpty()){
                res.append(" ");
            }
        }
        return res.toString();
    }
}