Reverse an array without affecting special characters - GeeksforGeeks

Reverse an array without affecting special characters - GeeksforGeeks
Given a string, that contains special character together with alphabets ('a' to 'z' and 'A' to 'Z'), reverse the string in a way that special characters are not affected.

Input:   str = "a,b$c"
Output:  str = "c,b$a"
Note that $ and , are not moved anywhere.  
Only subsequence "abc" is reversed

Simple Solution:
1) Create a temporary character array say temp[].
2) Copy alphabetic characters from given array to temp[].
3) Reverse temp[] using standard string reversal algorithm.
4) Now traverse input string and temp in a single loop. Wherever there is alphabetic character is input string, replace it with current character of temp[].

Efficient Solution:

1) Let input string be 'str[]' and length of string be 'n'
2) l = 0, r = n-1
3) While l is smaller than r, do following
    a) If str[l] is not an alphabetic character, do l++
    b) Else If str[r] is not an alphabetic character, do r--
    c) Else swap str[l] and str[r]

void reverse(char str[])

{

    // Initialize left and right pointers

    int r = strlen(str) - 1, l = 0;

 

    // Traverse string from both ends until

    // 'l' and 'r'

    while (l < r)

    {

        // Ignore special characters

        if (!isAlphabet(str[l]))

            l++;

        else if(!isAlphabet(str[r]))

            r--;

 

        else // Both str[l] and str[r] are not spacial

        {

            swap(str[l], str[r]);

            l++;

            r--;

        }

    }

}

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