Niuke bm83 string deformation (case conversion, string inversion, string replacement)

• subject ：BM83 String deformation

Ideas

• Convert case . Traversal string , Encountered lowercase letters , Convert to uppercase , Encountered a capital letter , Convert to lowercase , When encountering spaces, it is normal and unchanged .
• Invert the entire string .
• Bounded by spaces , Invert each word individually .

import java.util.*;

public class Solution {
    
    public String trans(String s, int n) {
    
        // write code here
        int len = s.length();
        StringBuilder res = new StringBuilder(len);
        //  First step ： Convert case 
        for(int i = 0; i < len; ++i){
    
            char cur = s.charAt(i);
            if(cur >= 'a' && cur <= 'z'){
    
                res.append((char)(cur - 'a' + 'A')); //  Lowercase to uppercase 
            } else if(cur >= 'A' && cur <= 'Z'){
    
                res.append((char)(cur - 'A' + 'a'));  //  Capitalize to lowercase 
            } else{
    
                res.append(cur);  //  Space 
            }
        }
        //  The second step ： Flip the entire string 
        res = res.reverse();
        //  The third step ： Flip a single word 
        int i = 0;
        int j = 0;
        while(i < len){
    
            j = i;  //  Point to space 
            //  With space as the boundary , Flip a word 
            while(j < len && res.charAt(j) != ' '){
    
                ++j;
            }
            //  Intercept [i, j) Substring of interval 
            StringBuilder word = new StringBuilder(res.substring(i, j));
            word = word.reverse();  //  Flip Words 
            res.replace(i, j, word.toString());  //  Replace the original word 
            i = j + 1;  //  Start with the next word 
        }
        return res.toString();
    }
}

summary

• Lowercase to uppercase ：ch = ch - 'a' + 'A'
• Capitalize to lowercase ：ch = ch - 'A' + 'a'
• String inversion ：str = str.reverse()
• Intercept substring ：sub = str.substring(start, end)
• Substring substitution ：str.replace(start, end, str1)