2000. Reverse Prefix of Word

Problem Link: https://leetcode.com/problems/reverse-prefix-of-word/description/

Given a 0-indexed string word and a character ch, reverse the segment of word that starts at index 0 and ends at the index of the first occurrence of ch (inclusive). If the character ch does not exist in word, do nothing.

• For example, if word = "abcdefd" and ch = "d", then you should reverse the segment that starts at 0 and ends at 3 (inclusive). The resulting string will be "dcbaefd".

Return the resulting string.

Example 1:

Input: word = "abcdefd", ch = "d"
Output: "dcbaefd"
Explanation: The first occurrence of "d" is at index 3. 
Reverse the part of word from 0 to 3 (inclusive), the resulting string is "dcbaefd".

Example 2:

Input: word = "xyxzxe", ch = "z"
Output: "zxyxxe"
Explanation: The first and only occurrence of "z" is at index 3.
Reverse the part of word from 0 to 3 (inclusive), the resulting string is "zxyxxe".

Example 3:

Input: word = "abcd", ch = "z"
Output: "abcd"
Explanation: "z" does not exist in word.
You should not do any reverse operation, the resulting string is "abcd".

Constraints:

• 1 <= word.length <= 250

• word consists of lowercase English letters.

• ch is a lowercase English letter.

Explanation:

Method 1:

Given string s= “abcdefd” and character ch = “d”

Step 1:

First find out the “ch” in given string “s”.

For finding character in a string there is one method in the java is indexOf(). The method return the index of the character.

If character not found in the string then it return -1.

Step 2:

Take StringBuilder class

append the string start from 0 to indexOf(ch)

Example: append(s, 0, indexOf(ch)+1);

Here It append the string from 0 to end-1.

Step 3:

Reverse the string stored in the StringBuilder object.

Step 4:

After reversing the string the remaining part of the original string is added.

start from indexOf(ch)+1 to String.length();

Step 5:

Finally print the string.

CODE:

public class ReversePrefixWord {
  public static void main(String[] args) {
    String s = "abcdefxy";
    char ch = 'd';
    System.out.println("Original String: "+s);
    System.out.println("After reversing prefix: "+reversePrefix(s,ch));
  }

  public static String reversePrefix(String word, char ch) {

    int i = word.indexOf(ch);
    StringBuilder sb = new StringBuilder();
    // Here length of the stirng length is 0 or below then return the original string
    if(i < 0){
      return word;
    }
    //appending the array from 0 to index of character in string.
    else{
      sb.append(word, 0, i+1);
    }

    //reverse the string
    sb.reverse();
    //then append the index+1 to string length.
    sb.append(word,i+1, word.length());

    return sb.toString();
  }
}

Original String: abcdefxy
After reversing prefix: dcbaefxy

Solution Link: https://leetcode.com/problems/reverse-prefix-of-word/submissions/1057005747/

Method 2:

Step 1:

First find out the “ch” in given string “s”.

For finding character in a string there is one method in the java is indexOf(). The method return the index of the character.

If character not found in the string then it return -1.

Step 2:

create a StringBuilder object and append the given string to the object.

Starting index left =0

Step 3:

swap the left ang right characters in the specified string left at 0 and right at s.charAt(ch);

In between the left and right swap the characters.

Here I used a method “setCharAt(index,character)”

It will take index and character. At mentioned index place the given character. swap the left and right characters

Step 4:

Print the final reversed prefix string.

CODE:

public class ReversePrefixWord {
  public static void main(String[] args) {
    String s = "abcdefxy";
    char ch = 'd';
    // System.out.println(s.indexOf(ch));
    System.out.println("Original String: "+s);
    System.out.println("After reversing prefix: "+reversePrefix(s,ch));
  }

  public static String reversePrefix(String s,char ch){
    //step 1
    int right = s.indexOf(ch);

    //step 2
    StringBuilder sb = new StringBuilder(s);
    int left=0;

    //step 3
    while(left<right){
      sb.setCharAt(left, s.charAt(right));
      sb.setCharAt(right, s.charAt(left));
      left++;
      right--;
    }

    return sb.toString();
  }
}

output:

Original String: abcdefxy
After reversing prefix: dcbaefxy

Solution Link: https://leetcode.com/problems/reverse-prefix-of-word/submissions/1106648987/

Method 3:

Step 1:

First find out the “ch” in given string “s”.

For finding character in a string there is one method in the java is indexOf(). The method return the index of the character.

If character not found in the string then it return -1.

Step 2:

calling the reverse method.

You can prefer the below link for explanation on reverse of a string

https://sirishachallagiri.hashnode.dev/reverse-of-a-string

CODE:

class Solution {
    public static void main(String[] args) {
    String s = "abcdefxy";
    char ch = 'd';
    // System.out.println(s.indexOf(ch));
    System.out.println("Original String: "+s);
    System.out.println("After reversing prefix: "+reversePrefix(s,ch));
  }

  public String reversePrefix(String word, char ch) {
      int x=word.indexOf(ch);
      return reverse(word,x);
  }

  public static String reverse(String s,int k){
      char[] c = s.toCharArray();
      for(int i=0,j=k;i<k/2;i++,j--){
          char temp=c[i];
          c[i]=c[j];
          c[j]=temp;
      }
      return new String(c);
  }
}

Output:

Original String: abcdefxy
After reversing prefix: dcbaefxy

Solution Link: https://leetcode.com/problems/reverse-prefix-of-word/submissions/1106655046/

Thank you for reading.

Happy Coding :)