Let’s see an approach to reverse words of a given String in Java without using any of the String library function Examples:
Input : "Welcome to neveropen" Output : "neveropen to Welcome" Input : "I love Java Programming" Output :"Programming Java love I"
Prerequisite: Regular Expression in Java
Java
// Java Program to reverse a String // without using inbuilt String function import java.util.regex.Pattern; public class Exp { // Method to reverse words of a String static String reverseWords(String str) { // Specifying the pattern to be searched Pattern pattern = Pattern.compile("\\s"); // splitting String str with a pattern // (i.e )splitting the string whenever their // is whitespace and store in temp array. String[] temp = pattern.split(str); String result = ""; // Iterate over the temp array and store // the string in reverse order. for (int i = 0; i < temp.length; i++) { if (i == temp.length - 1) result = temp[i] + result; else result = " " + temp[i] + result; } return result; } // Driver methods to test above method public static void main(String[] args) { String s1 = "Welcome to neveropen"; System.out.println(reverseWords(s1)); String s2 = "I love Java Programming"; System.out.println(reverseWords(s2)); } } |
Output:
neveropen to Welcome Programming Java love I
Time Complexity: O(n), where n is the length of the string.
Auxiliary Space: O(n)
Approach: Without using split() or trim()
By this approach, we can even remove extra trailing spaces and in between the words also.
Basically, this algorithm involves 3 steps.
- If you find white space, there can be two possibilities.
- It might be end of a word or else extra trailing space in between the words.
- if it is not a white space, add the character to temporary word as shown in the below code.
Below is the implementation of above approach.
Java
import java.util.*;class GFG { public static String reverseString(String s) { StringBuilder ans=new StringBuilder(); String temp = ""; for(int i=0;i<s.length();i++) { char ch = s.charAt(i); if(ch==' ') { //if we find white space add temp in the start if(!temp.equals("")) { //adding in the front every time ans.insert(0,temp+" "); } temp = ""; } else temp += ch; } //just removing the extra space at the end of the ans return ans.toString().substring(0,ans.length()-1); } public static void main(String[] args) { String s1=" Welcome to Geeks For Geeks "; System.out.println("Before reversing length of string : "+s1.length()); String ans1=reverseString(s1); System.out.println("After reversing length of string : "+ans1.length()); System.out.println("\""+ans1+"\"\n"); String s2=" I Love Java Programming "; System.out.println("Before reversing length of string : "+s2.length()); String ans2=reverseString(s2); System.out.println("After reversing length of string : "+ans2.length()); System.out.println("\""+ans2+"\""); }}//This code is contributed by aeroabrar_31 |
Before reversing length of string : 34 After reversing length of string : 26 "Geeks For Geeks to Welcome" Before reversing length of string : 34 After reversing length of string : 23 "Programming Java Love I"
Time Complexity: O(N) N is length of string
Auxiliary Space: O(1)
You can find the c++ solution for Reverse words in a String here This article is contributed by Sumit Ghosh. If you like neveropen and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the neveropen main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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