Write a method to replace all spaces in a string with ‘%20’.

Algorithm:

1. Count the number of spaces during the first scan of the string.

2. Scan the string from start to end for each character:

If a space is encountered, store “%20”.

Else, store the character as it is in the newly shifted location.

package crack.coding.interview;

/**

 * This class is used to replace all the spaces by "%20" in a string.

 * @author rajesh.dixit

 */

public class ReplaceSpacesInString {

    

    

     /**

      * Replace spaces from String from "%20"

      * @param str

      * @return

      */

     private static String replaceSpaces(String str) {

           if(str==null) {

                return null;

           }

          

           int len = str.length();

           int count = 0;

          

           /* Count all the spaces in the String. */

           for(int i=0;i<len;i++) {

                if(str.charAt(i) == ' ') {

                     count ++;

                }

           }

          

           /* Calculate the length of new String and define the new Char array. */

           int newLen = len + 2 * count;

           char[] newCharArray = new char[newLen];

           int j = 0;

          

           for(int i=0;i<len;i++) {

                char ch = str.charAt(i);

                if(' ' == ch) {

                     newCharArray[j++] = '%';

                     newCharArray[j++] = '2';

                     newCharArray[j++] = '0';

                } else {

                     newCharArray[j++] = ch;

                }

           }

           return new String(newCharArray);

     }

    

     /**

      * Driver Method

      * @param args

      */

     public static void main(String[] args) {

           String str = "replace space from string";

           String newStr = replaceSpaces(str);

           System.out.println(newStr);

     }

}