[Leetcode online programming record-1] string inversion by word

Preface

Leetcode (Address: https://oj.leetcode.com/) is an online programming site, typical questions, test cases complete, a total of 157 algorithm class questions. Afterwards, I will record some of my exercise questions. Some of my answers are self-made (original, or probably seen elsewhere) and some are from the discussion board, I will clearly mark the source.

Reverse words in a string

Given an input string, reverse the string word by word.

For example,
Given S = "the sky is blue ",
Return "Blue is sky ".

Click to show clarification.

Clarification:

• What constitutes a word?
  A sequence of non-space characters constitutes a word.
• Cocould the input string contain leading or trailing spaces?
  Yes. However, your reversed string shocould not contain leading or trailing spaces.
• How about multiple spaces between two words?
  Reduce them to a single space in the reversed string.

[My analysis] I used to reverse all strings and then reverse them by words, but the difficulty was how to deal with multiple spaces.

[Analysis 1-non-original] There may be multiple spaces between words. The character temp is scanned from the past and the result is returned:

1) if it is not a space, word + = temp;

2) if it is a space, append word to the front of result.

Reference: https://oj.leetcode.com/discuss/10888/my-java-solution-few-lines

/* Method 1: The second-level cache concept. Word is used to store characters. In case of space, if word is not a space, add word to the front of newstr of the string, set it to "" */public static string reversewords4 (string s) {string temp = ""; string result = ""; for (INT I = 0; I <S. length (); I ++) {char c = S. charat (I); If (C = '') {If (temp! = "" & Result! = "") {Result = temp + "" + result;} If (temp! = "" & Result = "") {result = temp;} temp = "" ;}else {temp + = C ;}} /* Last add */If (temp! = "" & Result! = "") {Result = temp + "" + result;} If (temp! = "" & Result = "") {result = temp;} return result ;}

[Analysis 2-non-original] use regular expressions to separate strings into string arrays. This requires system functions.

Reference: https://oj.leetcode.com/discuss/9142/my-accepted-java-solution

Solution 1: system functions trim () and split ()

/* Regular Expression \ s + represents any number of blank characters */public static string reversewords3 (string s) {string [] parts = S. trim (). split ("\ s +"); string out = ""; if (parts. length> 0) {for (INT I = parts. length-1; I> 0; I --) {out + = parts [I] + "";} out + = parts [0];} return out ;}

Solution 2: The default constructor of the system category separates strings by blank characters.

 public String reverseWords(String s) {        Scanner parts = new Scanner(s);         String result = "";         while(parts.hasNext()){            result = parts.next() + " " + result;        }         return result.trim();    }

[Leetcode online programming record-1] string inversion by word