LeetCode – Reverse Words in a String (Java)
Given an input string, reverse the string word by word.
For example, given s = "the sky is blue", return "blue is sky the".
Java Solution
This problem is pretty straightforward. We first split the string to words array, and then iterate through the array and add each element to a new string. Note: StringBuilder should be used to avoid creating too many Strings. If the string is very long, using String is not scalable since String is immutable and too many objects will be created and garbage collected.
class Solution { public String reverseWords(String s) { if (s == null || s.length() == 0) { return ""; } // split to words by space String[] arr = s.split(" "); StringBuilder sb = new StringBuilder(); for (int i = arr.length - 1; i >= 0; --i) { if (!arr[i].equals("")) { sb.append(arr[i]).append(" "); } } return sb.length() == 0 ? "" : sb.substring(0, sb.length() - 1); } } |
<pre><code> String foo = "bar"; </code></pre>
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Wrong, this is required to be done in place – reverse the whole thing, then reverse individual words
Hi, in your for loop if (!arr[i].equals(“”)) , why you judge “” instead of ” “? Isn’t that it should check if a string in the array contains spaces?
public static String reverseWords2(String s)
{
String[] tab = s.split(” “);
String temp = “”;
for(int i = 0; i<tab.length/2 ; i++)
{
temp = tab[i];
tab[i] = tab[(tab.length-1)-i];
tab[(tab.length-1)-i] = temp;
}
return Arrays.toString(tab);
}
public static String reverseWords2(String s)
{
String[] tab = s.split(” “);
String temp = “”;
for(int i = 0; i<tab.length/2 ; i++)
{
temp = tab[i];
tab[i] = tab[(tab.length-1)-i];
tab[(tab.length-1)-i] = temp;
}
StringBuffer result = new StringBuffer();
for (int i = 0; i < tab.length; i++)
{
result.append(tab[i]).append(" ");
}
return result.toString();
}
public static String reverseWords2(String s)
{
String[] tab = s.split(” “);
String temp = “”;
for(int i = 0; i<tab.length/2 ; i++)
{
temp = tab[i];
tab[i] = tab[(tab.length-1)-i];
tab[(tab.length-1)-i] = temp;
}
StringBuffer result = new StringBuffer();
for (int i = 0; i < tab.length; i++)
{
result.append(tab[i]).append(" ");
}
return result.toString();
}
package com.exam;
import java.util.*;
public class MyComparator{
public String comp(String s){
char []ch=s.toCharArray();
StringBuilder sb=new StringBuilder();
for(int i=ch.length-1;i>=0;i–){
sb.append(ch[i]);
}
String m=sb.toString();
return m;
}
public static void main(String args[]){
String s=(“ramesh”);
MyComparator mc=new MyComparator();
String ss=mc.comp(s);
System.out.println(ss);
}
}
import java.util.*;
class Demo
{
public static void main(String args[])
{
Scanner s=new Scanner(System.in);
System.out.println(“Enter any String:”);
String ss=s.nextLine();
String sb= new StringBuffer(ss).reverse().toString();
System.out.println(“before reverse:” + ss);
System.out.println(“after reverse:” + sb);
}
}
import java.util.*;
class Demo
{
public static void main(String args[])
{
Scanner s=new Scanner(System.in);
System.out.println(“Enter any String:”);
String ss=s.nextLine();
String sb= new StringBuffer(ss).reverse().toString();
System.out.println(“before reverse:” + ss);
System.out.println(“after reverse:” + sb);
}
}
One can also use ArrayDeque instead String[], which will much more flexible since it provides FirstAdd(), LastAdd(), LastRemove() and FirstRemove() methods.
ss = “Hello World”
sb = “dlroW olleH”
Requirement specification of this program:
ss =”Hello World”
sb = “World Hello”
public String reverseStringEffective(String input) {
StringBuilder sb= new StringBuilder();
if (input != null || input.length() != 0) {
String[] reverse = input.split(” “);
for (int i = reverse.length – 1; i >= 0; i–) {
sb.append(reverse[i]);
if (i > 0) {
sb.append(” “);
}
}
}return sb.toString();
Would this solution not work?
public String reverseWordsInStringProblem(String inputData) {
StringBuffer result = new StringBuffer(“”);
String[] parts = inputData.split(” “);
for (int i = parts.length – 1; i >= 0; i–) {
result.append(parts[i]).append(” “);
}
return result.toString();
}
String in Java is immutable, you know that right?
This should work to:
public static String reverseString(String input){
StringBuffer result = new StringBuffer();
StringTokenizer tokens = new StringTokenizer(input,” “);
while(tokens.hasMoreElements()){
result.insert(0, tokens.nextToken() + ” “);
}
return result.toString().trim();
}
You give me a very simple ans thanks
This is horrible.
private static String reverse(String s)
{
String[] tmp = s.split(” “);
s = “”;
for(int i=0; i<tmp.length; i++)
s = s+tmp[tmp.length-i-1]+" ";
return s.trim();
}
And horrible formatting (skills)
This is not the same.
reverseWord(String s){
index = s.indexOf(” “);
return index == -1?s : reverseWord(s.substring(index+1)) + ” “+s.substring(0,index);
}
Here a solution using trim() and replaceAll()
public String reverseWords(String s) {
StringBuilder result = new StringBuilder();
s = s.trim().replaceAll(” +”, ” “);
String[] arr = s.split(” “);
System.out.println(arr.length);
for (int i = 0; i < arr.length; i++) result.append(arr[arr.length – i – 1]).append(" ");
return (result.toString()).substring(0, result.length() – 1);
}
public static void main(String[] args) {
String s=”Hello world how’s it going”;
String[] s1=s.split(” “);
StringBuffer reverse=new StringBuffer(” “);
for(int i=(s1.length)-1;i>=0;i–){
reverse.append(s1[i]);
reverse.append(” “);
}
System.out.println(reverse);
}
much easier
before reverse:this is band
after reverse:dnab si siht
Hi Guys , here in above solution they are using string builder class …what if we are asked to print without using any additional java class object…below is the simple solution :-
public void word_rev(String str)
{
if(str.length()==0)
return ;
int k = str.length()-1 ;
int n = k ;
while(n>=0)
{
while(str.charAt(k)!=’ ‘)
{
if(k==0)
break ;
k– ;
}
if(k==0)
{
System.out.print(str.substring(k , n+1));
break ;
}
else
{
System.out.print(str.substring(k+1 , n+1));
System.out.print(” “);
}
n = k– ;
}
}
String str=”this is a line”;
String str1[]=str.split(” “);
String finalstr=” “;
for(int i=str1.length-1;i>=0;–i)
{
finalstr+=str1[i]+” “;
}
System.out.prntln(finalstr);
public class Testcase {
public static void main(String[] args) {
String t = “my name is dolly”;
String c[] = t.split(” “);
//System.out.println(c.length);
//System.out.println(c[0] + c[1] + c[2]);
for(int i =0;i=1;j–){
System.out.print(c[i].charAt(j-1));
}
System.out.print(” “);
}
}
}
Only one line in Python: https://github.com/renzon/code_interview_training/blob/master/reverse_words.py
private static void reverse_words(String input) {
int i;
System.out.println(“Input is “+input);
StringBuilder sb = new StringBuilder();
String[] temp = input.split(” “);
for (i = temp.length – 1 ; i>= 0; i–)
{
sb.append(temp[i]);
sb.append(” “);
}
System.out.println(“Reversed string is “+sb);
}
public static void main(String[] args) {
String str = "my name is melad";
Stack stack = new Stack();
String[] strArray = str.split(" ");
for (String s : strArray) {
stack.push(s);
}
StringBuilder sb = new StringBuilder();
while (!stack.empty()) {
sb.append(stack.pop()).append(" ");
}
System.out.println(sb);
}
using stack
Can someone tell me what will be the complexity of this?