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Compare two strings considering only alphanumeric characters

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  • Difficulty Level : Medium
  • Last Updated : 23 Jun, 2022

Given two strings that can contain lower and uppercase alphabets, numbers and special characters like dots, blank spaces, commas, etc. Compare both strings considering only alphanumeric characters([a-b], [A-B] and [0-9]) if they are equal or not. For example, strings “Ram, Shyam” and “Ram-Shyam” both are the same and also “/.’;[]” and “@# >” are same.

Examples: 

Input: str1 = "Ram, Shyam", str2 = " Ram - Shyam."
Output: Equal
Explanation: 
if we ignore all characters 
except alphanumeric characters 
then strings will be, 
str1 = "RamShyam" and str2 = "RamShyam". 
Therefore both strings are equal.

Input : str1 = "aaa123", str2 = "@aaa-12-3"
Output : Equal

Input : str1 = "abc123", str2 = "123abc"
Output : Unequal
Explanation: 
In this, str1 = "abc123" and str2 = "123abc". 
Therefore both strings are not equal.

Since we have to compare only alphanumeric characters therefore whenever any other character is found simply ignore it by increasing iterator pointer. For doing it simply take two integer variables i and j and initialize them by 0. Now run a loop to compare each and every character of both strings. Compare one by one if the character is alphanumeric otherwise increase the value of i or j by one.

Below is the implementation of the above approach:  

C++




#include <iostream>
using namespace std;
 
// Function to check alphanumeric equality of both strings
bool CompareAlphanumeric(string& str1, string& str2)
{
    // variable declaration
    int i, j;
    i = 0;
    j = 0;
 
    // Length of first string
    int len1 = str1.size();
 
    // Length of second string
    int len2 = str2.size();
 
    // To check each and every characters of both string
    while (i <= len1 && j <= len2) {
 
        // If the current character of the first string is not an
        // alphanumeric character, increase the pointer i
        while (i < len1
               && (!((str1[i] >= 'a' && str1[i] <= 'z')
                     || (str1[i] >= 'A' && str1[i] <= 'Z')
                     || (str1[i] >= '0' && str1[i] <= '9')))) {
            i++;
        }
 
        // If the current character of the second string is not an
        // alphanumeric character, increase the pointer j
        while (j < len2
               && (!((str2[j] >= 'a' && str2[j] <= 'z')
                     || (str2[j] >= 'A' && str2[j] <= 'Z')
                     || (str2[j] >= '0' && str2[j] <= '9')))) {
            j++;
        }
 
        // if all alphanumeric characters of both strings are same
        // then return true
        if (i == len1 && j == len2)
            return true;
 
        // if any alphanumeric characters of both strings are not same
        // then return false
        else if (str1[i] != str2[j])
            return false;
 
        // If current character matched,
        // increase both pointers to check the next character
        else {
            i++;
            j++;
        }
    }
 
    // If not same, then return false
    return false;
}
 
// Function to print Equal or Unequal if strings are same or not
void CompareAlphanumericUtil(string str1, string str2)
{
    bool res;
 
    // check alphanumeric equality of both strings
    res = CompareAlphanumeric(str1, str2);
 
    // if both are alphanumeric equal, print Equal
    if (res == true)
        cout << "Equal" << endl;
 
    // otherwise print Unequal
    else
        cout << "Unequal" << endl;
}
 
// Driver code
int main()
{
 
    string str1, str2;
 
    str1 = "Ram, Shyam";
    str2 = " Ram - Shyam.";
    CompareAlphanumericUtil(str1, str2);
 
    str1 = "abc123";
    str2 = "123abc";
    CompareAlphanumericUtil(str1, str2);
 
    return 0;
}

Java




// Java implementation of the approach
import java.util.*;
 
class GFG
{
 
// Function to check alphanumeric
// equality of both strings
static boolean CompareAlphanumeric(char[] str1,
                                   char[] str2)
{
    // variable declaration
    int i, j;
    i = 0;
    j = 0;
 
    // Length of first string
    int len1 = str1.length;
 
    // Length of second string
    int len2 = str2.length;
 
    // To check each and every characters
    // of both string
    while (i <= len1 && j <= len2)
    {
 
        // If the current character of the first string is not an
        // alphanumeric character, increase the pointer i
        while (i < len1 && (!((str1[i] >= 'a' && str1[i] <= 'z') ||
                              (str1[i] >= 'A' && str1[i] <= 'Z') ||
                              (str1[i] >= '0' && str1[i] <= '9'))))
        {
            i++;
        }
 
        // If the current character of the second string is not an
        // alphanumeric character, increase the pointer j
        while (j < len2 && (!((str2[j] >= 'a' && str2[j] <= 'z') ||
                              (str2[j] >= 'A' && str2[j] <= 'Z') ||
                              (str2[j] >= '0' && str2[j] <= '9'))))
        {
            j++;
        }
 
        // if all alphanumeric characters of
        // both strings are same then return true
        if (i == len1 && j == len2)
        {
            return true;
        }
         
        // if any alphanumeric characters of
        // both strings are not same then return false
        else if (str1[i] != str2[j])
        {
            return false;
        }
         
        // If current character matched,
        // increase both pointers to
        // check the next character
        else
        {
            i++;
            j++;
        }
    }
 
    // If not same, then return false
    return false;
}
 
// Function to print Equal or Unequal
// if strings are same or not
static void CompareAlphanumericUtil(String str1,
                                    String str2)
{
    boolean res;
 
    // check alphanumeric equality of both strings
    res = CompareAlphanumeric(str1.toCharArray(),
                              str2.toCharArray());
 
    // if both are alphanumeric equal,
    // print Equal
    if (res == true)
    {
        System.out.println("Equal");
    }
     
    // otherwise print Unequal
    else
    {
        System.out.println("Unequal");
    }
}
 
// Driver code
public static void main(String[] args)
{
    String str1, str2;
 
    str1 = "Ram, Shyam";
    str2 = " Ram - Shyam.";
    CompareAlphanumericUtil(str1, str2);
 
    str1 = "abc123";
    str2 = "123abc";
    CompareAlphanumericUtil(str1, str2);
}
}
 
// This code is contributed by Rajput-Ji

Python3




# Function to check alphanumeric equality
# of both strings
def CompareAlphanumeric(str1, str2):
     
    # variable declaration
    i = 0
    j = 0
 
    # Length of first string
    len1 = len(str1)
 
    # Length of second string
    len2 = len(str2)
 
    # To check each and every character of both string
    while (i <= len1 and j <= len2):
         
        # If the current character of the first string
        # is not an alphanumeric character,
        # increase the pointer i
        while (i < len1 and
              (((str1[i] >= 'a' and str1[i] <= 'z') or
                (str1[i] >= 'A' and str1[i] <= 'Z') or
                (str1[i] >= '0' and str1[i] <= '9')) == False)):
            i += 1
 
        # If the current character of the second string
        # is not an alphanumeric character,
        # increase the pointer j
        while (j < len2 and
              (((str2[j] >= 'a' and str2[j] <= 'z') or
                (str2[j] >= 'A' and str2[j] <= 'Z') or
                (str2[j] >= '0' and str2[j] <= '9')) == False)):
            j += 1
 
        # if all alphanumeric characters of
        # both strings are same, then return true
        if (i == len1 and j == len2):
            return True
 
        # if any alphanumeric characters of
        # both strings are not same, then return false
        elif (str1[i] != str2[j]):
            return False
 
        # If current character matched,
        # increase both pointers
        # to check the next character
        else:
            i += 1
            j += 1
 
    # If not same, then return false
    return False
 
# Function to print Equal or Unequal
# if strings are same or not
def CompareAlphanumericUtil(str1, str2):
     
    # check alphanumeric equality of both strings
    res = CompareAlphanumeric(str1, str2)
 
    # if both are alphanumeric equal, print Equal
    if (res == True):
        print("Equal")
         
    # otherwise print Unequal
    else:
        print("Unequal")
 
# Driver code
if __name__ == '__main__':
    str1 = "Ram, Shyam"
    str2 = " Ram - Shyam."
    CompareAlphanumericUtil(str1, str2)
 
    str1 = "abc123"
    str2 = "123abc"
    CompareAlphanumericUtil(str1, str2)
 
# This code is contributed by Surendra_Gangwar

C#




// C# implementation of the approach
using System;
 
class GFG
{
     
    // Function to check alphanumeric
    // equality of both strings
    static bool CompareAlphanumeric(char []str1,
                                    char []str2)
    {
        // variable declaration
        int i, j;
        i = 0;
        j = 0;
     
        // Length of first string
        int len1 = str1.Length;
     
        // Length of second string
        int len2 = str2.Length;
     
        // To check each and every characters
        // of both string
        while (i <= len1 && j <= len2)
        {
     
            // If the current character of the first
            // string is not an alphanumeric character,
            // increase the pointer i
            while (i < len1 && (!((str1[i] >= 'a' && str1[i] <= 'z') ||
                                  (str1[i] >= 'A' && str1[i] <= 'Z') ||
                                  (str1[i] >= '0' && str1[i] <= '9'))))
            {
                i++;
            }
     
            // If the current character of the second
            // string is not an alphanumeric character,
            // increase the pointer j
            while (j < len2 && (!((str2[j] >= 'a' && str2[j] <= 'z') ||
                                  (str2[j] >= 'A' && str2[j] <= 'Z') ||
                                  (str2[j] >= '0' && str2[j] <= '9'))))
            {
                j++;
            }
     
            // if all alphanumeric characters of
            // both strings are same then return true
            if (i == len1 && j == len2)
            {
                return true;
            }
             
            // if any alphanumeric characters of
            // both strings are not same then return false
            else if (str1[i] != str2[j])
            {
                return false;
            }
             
            // If current character matched,
            // increase both pointers to
            // check the next character
            else
            {
                i++;
                j++;
            }
        }
     
        // If not same, then return false
        return false;
    }
     
    // Function to print Equal or Unequal
    // if strings are same or not
    static void CompareAlphanumericUtil(string str1,
                                        string str2)
    {
        bool res;
     
        // check alphanumeric equality of both strings
        res = CompareAlphanumeric(str1.ToCharArray(),
                                  str2.ToCharArray());
     
        // if both are alphanumeric equal,
        // print Equal
        if (res == true)
        {
            Console.WriteLine("Equal");
        }
         
        // otherwise print Unequal
        else
        {
            Console.WriteLine("Unequal");
        }
    }
     
    // Driver code
    public static void Main()
    {
        string str1, str2;
     
        str1 = "Ram, Shyam";
        str2 = " Ram - Shyam.";
        CompareAlphanumericUtil(str1, str2);
     
        str1 = "abc123";
        str2 = "123abc";
        CompareAlphanumericUtil(str1, str2);
    }
}
 
// This code is contributed by AnkitRai01

Javascript




<script>
 
    // JavaScript implementation of the approach
     
    // Function to check alphanumeric
    // equality of both strings
    function CompareAlphanumeric(str1, str2)
    {
        // variable declaration
        let i, j;
        i = 0;
        j = 0;
      
        // Length of first string
        let len1 = str1.length;
      
        // Length of second string
        let len2 = str2.length;
      
        // To check each and every characters
        // of both string
        while (i <= len1 && j <= len2)
        {
      
            // If the current character of the first
            // string is not an alphanumeric character,
            // increase the pointer i
            while (i < len1 &&
            (!((str1[i].charCodeAt() >= 'a'.charCodeAt() &&
            str1[i].charCodeAt() <= 'z'.charCodeAt()) ||
            (str1[i].charCodeAt() >= 'A'.charCodeAt() &&
            str1[i].charCodeAt() <= 'Z'.charCodeAt()) ||
            (str1[i].charCodeAt() >= '0'.charCodeAt() &&
            str1[i].charCodeAt() <= '9'.charCodeAt()))))
            {
                i++;
            }
      
            // If the current character of the second
            // string is not an alphanumeric character,
            // increase the pointer j
            while (j < len2 &&
            (!((str2[j].charCodeAt() >= 'a'.charCodeAt() &&
            str2[j].charCodeAt() <= 'z'.charCodeAt()) ||
            (str2[j].charCodeAt() >= 'A'.charCodeAt() &&
            str2[j].charCodeAt() <= 'Z'.charCodeAt()) ||
            (str2[j].charCodeAt() >= '0'.charCodeAt() &&
            str2[j].charCodeAt() <= '9'.charCodeAt()))))
            {
                j++;
            }
      
            // if all alphanumeric characters of
            // both strings are same then return true
            if (i == len1 && j == len2)
            {
                return true;
            }
              
            // if any alphanumeric characters of
            // both strings are not same then return false
            else if (str1[i] != str2[j])
            {
                return false;
            }
              
            // If current character matched,
            // increase both pointers to
            // check the next character
            else
            {
                i++;
                j++;
            }
        }
      
        // If not same, then return false
        return false;
    }
      
    // Function to print Equal or Unequal
    // if strings are same or not
    function CompareAlphanumericUtil(str1, str2)
    {
        let res;
      
        // check alphanumeric equality of both strings
        res = CompareAlphanumeric(str1.split(''),
                                  str2.split(''));
      
        // if both are alphanumeric equal,
        // print Equal
        if (res == true)
        {
            document.write("Equal" + "</br>");
        }
          
        // otherwise print Unequal
        else
        {
            document.write("Unequal");
        }
    }
     
    let str1, str2;
      
    str1 = "Ram, Shyam";
    str2 = " Ram - Shyam.";
    CompareAlphanumericUtil(str1, str2);
 
    str1 = "abc123";
    str2 = "123abc";
    CompareAlphanumericUtil(str1, str2);
 
</script>

Output: 

Equal
Unequal

 

Time Complexity: O(n*n)
Auxiliary Space: O(1), as no extra space is required


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