[sword finger offer] 58 - I. flip the word order

The finger of the sword Offer 58 - I. Flip word order

subject

  Enter an English sentence , Turn over the order of the words in the sentence , But the order of the characters in the word is the same . For the sake of simplicity , Punctuation is treated like ordinary letters . For example, input string "I am a student. “, The output "student. a am I”.

Ideas

  Double pointer , Flashback traversal string s, Record the left and right index boundaries of words i,j. Determine the boundary of one word at a time , Just add it to the word list res in , Final , Splice the word list into a string , And return .

Code

class Solution {
    
    public String reverseWords(String s) {
    
        s = s.trim();//  Delete leading and trailing spaces 
        int j = s.length() - 1,i = j; 

        StringBuilder res = new StringBuilder();

        //  Search back and forth 
        // "hello world"
        while(i >= 0)
        {
    
            while(i >= 0 && s.charAt(i) != ' ') i--;//  Search for the first space   Space encountered i stop searching 

            //  Split string   from i + 1 Start is not a space   And then to j Location （j+1 Can't get ）
            res.append(s.substring(i + 1,j + 1) + " ");//  Add words 

            while(i >= 0 && s.charAt(i) == ' ')
            {
    
                i--;//  Skip spaces between words 
            }

            //  to update j  Then move on to the next step i
            j = i;
        }

        return res.toString().trim();// Convert to string and return 
    }
}