16. String inversion

Title Description

• Input : " hello world! "
  Output : “world! hello”
  explain : The input string can contain extra spaces before or after , But the reversed characters cannot include .
• Input : “a good example”
  Output : “example good a”
  explain : If there are extra spaces between two words , Reduce the space between inverted words to just one .

public String reverseWords(String s) {
        String[] strs = s.trim().split(" ");//  Delete leading and trailing spaces , Split string 
        StringBuilder res = new StringBuilder();
        for(int i = strs.length - 1; i >= 0; i--){//  Traverse the word list in reverse order 
            if(strs[i].equals(" ")) continue;//  If you encounter an empty word, skip 
            res.append(strs[i] + " ");//  Splice words into  StringBuilder
        }
        return res.toString().trim();//  Convert to string , Delete trailing spaces , And back to 
    }

General idea ： Store the string in the array , Then traverse from the end of the array , But when traversing , When you encounter two spaces , At this time, we should ignore it , Continue traversing , At the same time, each character traversed is stored in StringBuilder, Finally, it is converted to string output .