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Reverse a string in place
  • Posted: 7 years ago
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Write a function to reverse a String in place without creating another String.


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  • Posted: 7 years ago
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  • Edit


  • Create a character array from the input String.
  • Take two pointers at the first and last index of the array. Interchange their values.
  • Move the pointers - the first one in forward direction and the second one in backward direction.
  • Repeat the last two steps while the first pointer is less than the second pointer.

Example - Let the input string be '\( algoqueue \)'.



Time complexity = \( O(n) \).

public string reverseString(String input){

     /* Input string is null */
     if (input == null)
         return null;

     /* string to character array */
     char[] string2CharArray = input.ToCharArray();
     /* First pointer */
     int firstIndex = 0;
     /* Second pointer */
     int lastIndex = input.length - 1;

     while (firstIndex  <  lastIndex){

         /* Exchange the values at the two pointer */
         char temp = string2CharArray[firstIndex];
         string2CharArray[firstIndex] = string2CharArray[lastIndex];
         string2CharArray[lastIndex] = temp;

         /* Move the first pointer forward */
         firstIndex ++;
         /* Move the second pointer backward */
         lastIndex --;
     }
     return String.valueOf(string2CharArray);
 }
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