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Reverse a string without affecting special characters


Given a string which contains special characters(such as %,&,*,^,$) and alphabets(‘a’ to ‘z’ and ‘A’ to ‘Z’), write a function that will reverse the string in a way that special characters are not affected


s = “[email protected]&d”

[email protected]&a”

Method 1(Simple Solution)


1. Create a auxilary string ‘t’ and store all the alphabetic characters in string ‘t’

2. Now, reverse the string ‘t’

3. Now, Traverse the input string and string ‘t’ at a time

a. If there is a alphabetic character in input string, then replace it with the character in string ‘t’
b. If the character in input string is not a alphabetic character, then just move to the next character

Method 2(Eficient Solution)

In this method we will be not using extra space


1. Traverse the input string with  two varaibles l and r where l =0 and r = n-1, n is the length of the input string

2.  while l < r

a. if s[l] is not a alphabet, then do l++
b. else if s[r] is not a alphabet, then do r–
c. else swap the characters in s[l] and s[r] and so l++, r–

using namespace std;
// Returns true if x is an aplhabatic character, false otherwise
bool isAlphabet(char x)
    return ( (x >= 'A' &&  x <= 'Z') ||
             (x >= 'a' &&  x <= 'z') );
void reverseString(char s[])
    // Initialize l and r
    int r = strlen(s) - 1, l = 0;
    //Till l meets r, travers from both ends
    while (l < r)
        // ignore special characters
        if (!isAlphabet(s[l]))
        else if(!isAlphabet(s[r]))
        else // if both s[l] and s[r] are alphabatical characters
            swap(s[l], s[r]);

int main()
    char s[] = "[email protected]&d";
    cout << "Input string: " << s << endl;
    cout << "Output string: " << s << endl;
    return 0;

Try It

READ  Longest Common Prefix using Trie


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