Reverse Only Alphabets Problem

Reverse Only Alphabets Problem

Given: A string containing special characters (!,@,^,&,$) and alphabets (‘a’ to ‘z’ and ‘A’ to ‘Z’). We have to reverse only the alphabets keeping the special symbols intact. 

Input: A@%gh,q

Output: q@%hg,A

Explanation: Here we have to reverse characters in the array and ignore the special symbols. Only the position of characters will change and position of special symbols will be same. 

# Approach 1(Efficient)

In this method, we will be not using extra space.

Code:

#include <iostream>
#include <string.h>

// Function returns 1 (true) if x is alphabet, 0 (false) otherwise
int check_alpha(char z)
{
  int flag = 0;
  if ((z >= 'A' && z <= 'Z') || (z >= 'a' && z <= 'z'))
    flag = 1;
  else
    flag = 0;
  if (flag == 0)
    return 0;
  else
    return 1;
}

// Function reverses a string
void revstring(char str[])
{
  // Initializing x and y
  int x = strlen(str) - 1, y = 0;
  // Traversing from both ends, till x &y are equal
  while (y < x)
  {
    // leave special characters
    if (!check_alpha(str[y]))
      y++;
    else if (!check_alpha(str[x]))
      x--;
    else
    // if both s[y] and s[x] are alphabatical characters
    // swap the alphabets
    {
      char temp;
      temp = str[y];
      str[y] = str[x];
      str[x] = temp;
      y++;
      x--;
    }
  }
}

int main()
{
  char str[] = "A@%gh&q";
  std::cout << "Input string: " << str << std::endl;
  revstring(str);
  std::cout << "Output string: " << str << std::endl;
  return 0;
}

Output

Input string: A@%gh&q
Output string: qhg%@A

# Approach 2

In this approach, we have to use extra space by making a new array like pass[].

Follow the following steps:-

1. Create a auxilary character array like pass[].
2. Now copy alphabets from given array to pass[].
3. Reversing pass[] using string reversal.
4. We traverse input string and pass in a single loop. When a alphabet character occurs in input string, replace it with present character of pass[].

Code

#include <iostream>
#include <string.h>

// Function returns 1 (true) if x is alphabet, 0 (false) otherwise
int check_alpha(char z)
{
  int flag = 0;
  if ((z >= 'A' && z <= 'Z') || (z >= 'a' && z <= 'z'))
    flag = 1;
  else
    flag = 0;
  if (flag == 0)
    return 0;
  else
    return 1;
}

// Function reverses a string
void revstring(char str[])
{
  // Initializing x and y
  int x = strlen(str) - 1, y = 0;
  // Traversing from both ends, till x &y are equal
  while (y < x)
  {
    char temp;
    temp = str[y];
    str[y] = str[x];
    str[x] = temp;
    y++;
    x--;
  }
}

int main()
{
  char str[] = "A@%gh&q";
  std::cout << "Input string: " << str << std::endl;

  // Create a auxiliary character array
  char pass[strlen(str)];
  // Copy alphabets from given array to pass[]
  int k = 0;
  for (int i = 0; i < strlen(str); i++)
  {
    if (check_alpha(str[i]))
    {
      pass[k] = str[i];
      k++;
    }
  }
  // Reverse pass[] using string reversal
  revstring(pass);
  // Traverse input string and pass in a single loop
  // When a alphabet character occurs in input string, 
  // replace it with present character of pass[]
  k = 0;
  for (int i = 0; i < strlen(str); i++)
  {
    if (check_alpha(str[i]))
    {
      str[i] = pass[k];
      k++;
    }
  }

  std::cout << "Output string: " << str << std::endl;
  return 0;
}

Output

Input string: A@%gh&q
Output string: qhg%@A