Ouput of Reversing words of String does not come as expected

Question

Given a String with words.Reverse words of String.

Sample Input 1

Hello World

Sample Output

World Hello

MyApproach

To reverse words I first counted how many spaces are there.After that I stored their space index in an array.Using lastIndex, I printed the last elements of the array.After that I printed the last 2 words of the array.

static String reverseWords(String inputString)
 {
    int l1=inputString.length();
    int count=1;
    for(int i=0;i<l1;i++)
    {
        char ch=inputString.charAt(i);
        if(ch==' ')
        {
            count++;
        }
    }
     
    int k=0;
    int[] spaceindex=new int[count];
    spaceindex[0]=0;
    k++;
    for(int i=0;i<l1;i++)
    {
        char ch=inputString.charAt(i);
        if(ch==' ')
        {
            spaceindex[k++]=i+1;
        }
    }
    
    int p=spaceindex.length-1;
    String strnew="";
    for(int j=spaceindex[p];j<l1;j++)
    {
        char c=inputString.charAt(j);
        strnew=strnew+c;
    }
    

    p--;
    while(p>=0)
    {
         for(int j=spaceindex[p];;j++)
            {
             
              char c=inputString.charAt(j);
               if(c==' ')
               {
                   break;
               }
               strnew=strnew+c;
                
            }   
         
    }
   return strnew;   
}

InputParameters     ActualOutput                        Expected Output

Hello World         WorldHelloWorldHello(Infinite loop) WorldHello

@Edit I asked Why the code I wrote is wrong.I tried without using any inbuilt functions(which was necessary for me).In that way I think It is not Duplicate Ans according to me.

Can anyone guide me what went wrong in my code.

You could use String.split to split on the space character, then just reverse the order of the array it gives you. — Arnaud, Dec 06 '15 at 08:35
When you step through you code in your debugger what do you see? Where do you change `p` inside your loop so it can stop? Can you try using the formatter in your IDE so your code is easier to read? — Peter Lawrey, Dec 06 '15 at 08:36
@Berger me too, whenever I answer a homework question without realizing it. ;) — Peter Lawrey, Dec 06 '15 at 08:39

Ahmad Alkhatib · Answer 1 · 2015-12-06T08:49:34.120

1

Simple solution :

public static void main(String[] args) {

    String x = "Hello World";
    String[] xArray = x.split(" ");
    String result = "";

    for (int i = xArray.length - 1; i >= 0; i--) {
        result += xArray[i] + " ";
    }
    System.out.println(result.trim()); // World Hello
   }

edited Dec 06 '15 at 08:49

answered Dec 06 '15 at 08:38

Ahmad Alkhatib

1,230
2
14
31

1

You have an extra space here. – Arnaud Dec 06 '15 at 08:39
i don't understand , can you explain where is the extra space please ? – Ahmad Alkhatib Dec 06 '15 at 08:44
The last appended word shouldn't be followed by a space, so there is an extra space at the end of the result String. – Arnaud Dec 06 '15 at 08:46
1

add .trim() to the result to be : System.out.println(result.trim() ); – Ahmad Alkhatib Dec 06 '15 at 08:47

Sacert · Accepted Answer · 2015-12-06T08:49:06.237

1

The issue within your code was the while loop:

 while(p>=0) {
        strnew = strnew + " ";
        for(int j=spaceindex[p];;j++) {
           char c=inputString.charAt(j);
           if(c==' '){
              break;
           }
           strnew=strnew+c;
        }   
        p--;
 }

Adding the p-- will prevent the loop for occurring infinitely. Also inserting the strnew = strnew + " "; after the while loop ensures a space in between each word.

edited Dec 06 '15 at 08:49

answered Dec 06 '15 at 08:43

Sacert

129
7

I think your Ans is perfect.Because you checked the code.+1 for that.Other Ans were correct obviously but They are for reference to make my hardcode a bit easy.Thank you for you work. – Jason arora Dec 06 '15 at 13:09

score 1 · Answer 3 · answered Dec 06 '15 at 08:45

It's possible without using another arrays, splits or any additional strucure.

Having array of characters ( convert if needed as String is immutable), first reverse all characters in the array. Secondly loop over spaces and for each word reverse characters in the word.

score 1 · Answer 4 · answered Dec 06 '15 at 09:02

You can use a StringTokenizer to convert the string into tokens or String.split function. You can push this collection into a Stack and extract the elements in a reverse order. To join the strings back you could use a StringBuilder or a StringBuffer.

To do this more efficiently you could convert the string to a character array and StringBuilders

String myString = "Here is the String";
char[] myChars = myString.toCharArray();

StringBuilder word = new StringBuilder();
StringBuilder newString = new StringBuilder();
for(int i = myChars.length - 1; --i >= 0;) {
   char c = myChars[i];
   if(c == ' ') {
       newString.append(c);
       newString.append(word);
       word = new StringBuilder();
   } else {
       word.append(c);
   }
}

score 1 · Answer 5 · answered Dec 06 '15 at 09:04

I would base an implementation on String.lastIndexOf(int) and String.substring(int, int). I'd got with a StringBuilder to construct the output "sentence" and a while loop to iterate the words in reverse order. Something like,

static String reverseWords(String in) {
    StringBuilder sb = new StringBuilder(in.length());
    int space;
    while ((space = in.lastIndexOf(' ')) > 0) {
        sb.append(in.substring(space + 1, in.length())).append(' ');
        in = in.substring(0, space);
    }
    sb.append(in);
    return sb.toString();
}

Which I tested with your provided sample

public static void main(String[] args) {
    System.out.println(reverseWords("Hello World"));
}

Getting (as expected)

World Hello

Ouput of Reversing words of String does not come as expected

Sample Input 1

Sample Output

5 Answers5