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Python | Count the Number of matching characters in a pair of string

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  • Difficulty Level : Easy
  • Last Updated : 20 Oct, 2022
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Given a pair of non-empty strings. Count the number of matching characters in those strings (consider the single count for the character which have duplicates in the strings). 

Examples:

Input : str1 = 'abcdef'
        str2 = 'defghia'
Output : 4 
(i.e. matching characters :- a, d, e, f)

Input : str1 = 'aabcddekll12@'
        str2 = 'bb22ll@55k'
Output : 5 
(i.e. matching characters :- b, 1, 2, @, k)

Approach 1: 1. Initialize a counter variable with 0. 2. Iterate over the first string from the starting character to ending character. 3. If the character extracted from first string is found in the second string and also first occurrence index of that extracted character in first string is same as that of index of current extracted character then increment the value of counter by 1.

Note: For this, use string.find(character) in python. This returns the first occurrence index of character in string, if found, otherwise return -1. For example : str=’abcdedde’ str.find(‘d’) –> 3 str.find(‘e’) –> 4 str.find(‘g’) –> -1

4. Output the value of counter. Below is the implementation of above approach. 

Python




// C++ code to count number of matching
// characters in a pair of strings
 
# include <bits/stdc++.h>
using namespace std
 
// Function to count the matching characters
void count(string str1, string str2)
{
    int c = 0, j = 0
 
    // Traverse the string 1 char by char
    for (int i=0
         i < str1.length()
         i++) {
 
        // This will check if str1[i]
        // is present in str2 or not
        // str2.find(str1[i]) returns - 1 if not found
        // otherwise it returns the starting occurrence
        // index of that character in str2
        if (str2.find(str1[i]) >= 0
            and j == str1.find(str1[i]))
        c += 1
        j += 1
    }
    cout << "No. of matching characters are: "
    << c / 2
}
 
// Driver code
int main()
{
    string str1 = "aabcddekll12@"
    string str2 = "bb2211@55k"
 
    count(str1, str2)
}


Output :

No. of matching characters are : 5

Approach 2: 1.In this approach set() is used to remove duplicate on a given string. 2.After that concept of set(intersection) is used on given string. 3.After that we find a length using len() method. 

Python3




# Python code to count number of unique matching
# characters in a pair of strings
 
# count function count the common unique
# characters present in both strings .
def count(str1 ,str2) :
    # set of characters of string1
    set_string1 = set(str1)
 
    # set of characters of string2
    set_string2 = set(str2)
 
    # using (&) intersection mathematical operation on sets
    # the unique characters present in both the strings
    # are stored in matched_characters set variable
    matched_characters = set_string1 & set_string2
 
    # printing the length of matched_characters set
    # gives the no. of matched characters
    print("No. of matching characters are : " + str(len(matched_characters)) )
 
 
# Driver code
if __name__ == "__main__" :
 
    str1 = 'aabcddekll12@'  # first string
    str2 = 'bb2211@55k'     # second string
 
    # call count function
    count( str1 , str2 )
    


Output :

No. of matching characters are : 5

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