Frequency of a substring in a string | Set 2

Given a string str of length N and a substring pattern of length M, the task is to find the frequency of occurrences of pattern as a substring in the given string. If pattern is present in the string str, then print "Yes" with the count of its occurrence. Otherwise, print "No".

Examples:

Input: str = "geeksforgeeks", pattern = "geeks"
Output: 2
Explanation:
The occurrence of the string "geeks" in the string "geeksforgeeks" is at index 0 and 8.
Therefore, the count is 2.

Input: str = "dhimanman", pattern = "max"
Output: 0

Naive Approach: Refer to the previous post for the simplest approach to solve the problem. Time Complexity: O(N*M)
Auxiliary Space: O(1)

Approach using KMP Algorithm: Refer to the previous post of this article to solve the problem using KMP algorithm. Time Complexity: O(N + M)
Auxiliary Space: O(M)

Approach using Regular Expression: Follow the steps below to solve the problem:

• Form the regular expression of the string pattern using regex() function.
• Create a smatch M using function smatch().
• Check the presence of the string pattern in the string str using function regex_match() as:

regex_search(str, m, c)
where, 
str is the given string, 
m is smatch, 
c is the regular expression of the string pattern.

• In the above steps, if the function regex_match() returns True, then print "Yes" and find the occurrence of the string pattern. Otherwise, print "No".
• Create a variable numberOfMatches of data type ptrdiff_t to store the count of occurrence.
• Find the numberOfMatches using function regex_iterator() function as:

ptrdiff_t numberOfMatches = std::distance(sregex_iterator(S.begin(), S.end(), c), sregex_iterator())

• Print the count of occurrence in the above steps as the result.

Below is the implementation of the above approach:

// C++ program for the above approach

#include <bits/stdc++.h>
using namespace std;

// Function to find the frequency of
// substring in the given string S
void find_frequency(string S, string pattern)
{
    // Create a regular expression
    // of the string pattern
    regex c(pattern);

    // Determines the matching behavior
    smatch m;

    // Use member function on 'm'
    // regex_search to check if
    // string X is present in S or not
    if (regex_search(S, m, c) == true) {
        cout << "Yes"
             << "\n";
    }
    else {
        cout << "No";
    }

    // Count the number of matches
    ptrdiff_t numberOfMatches = std::distance(
        sregex_iterator(S.begin(), S.end(), c),
        sregex_iterator());

    // Print the coun of occurrence
    cout << "Frequency of string " << pattern << " is "
         << numberOfMatches;
}
// Driver code
int32_t main()
{
    // Given string str and pattern
    string str = "geeksforgeeks";
    string pattern = "geeks";

    // Function Call
    find_frequency(str, pattern);

    return 0;
}

// Java program for the above approach

import java.util.regex.*;

class GFG {
    // Function to find the frequency of
    // substring in the given string S
    static void find_frequency(String S, String pattern)
    {
        // Create a regular expression
        // of the string pattern
        Pattern c = Pattern.compile(pattern);

        // Determines the matching behavior
        Matcher m = c.matcher(S);

        // Use member function on 'm'
        // find to check if string X
        // is present in S or not
        if (m.find()) {
            System.out.println("Yes");
        }
        else {
            System.out.println("No");
        }

        // Count the number of matches
        int numberOfMatches = 0;

        m.reset();

        while (m.find()) {
            numberOfMatches++;
        }

        // Print the count of occurrence
        System.out.println("Frequency of string " + pattern
                           + " is " + numberOfMatches);
    }

    // Driver code
    public static void main(String[] args)
    {
        // Given string str and pattern
        String str = "geeksforgeeks";
        String pattern = "geeks";

        // Function Call
        find_frequency(str, pattern);
    }
}

// Contributed by adityasha4x71

# Python program for the above approach

import re

def find_frequency(s, pattern):
    # Create a regular expression
    # of the string pattern
    c = re.compile(pattern)

    # Determines the matching behavior
    m = c.search(s)

    # Use member function on 'm'
    # find to check if string X
    # is present in S or not
    if m:
        print("Yes")
    else:
        print("No")

    # Count the number of matches
    numberOfMatches = 0

    m = c.finditer(s)

    for match in m:
        numberOfMatches += 1

    # Print the count of occurrence
    print("Frequency of string " + pattern
          + " is " + str(numberOfMatches))

# Driver code
if __name__ == "__main__":
    # Given string str and pattern
    s = "geeksforgeeks"
    pattern = "geeks"

    # Function Call
    find_frequency(s, pattern)


# This code is contributed by princekumaras

// C# program for the above approach
using System;
using System.Text.RegularExpressions;

class GFG {
    // Function to find the frequency of
    // substring in the given string S
    static void find_frequency(string S, string pattern)
    {
        // Create a regular expression
        // of the string pattern
        Regex c = new Regex(pattern);

        // Determines the matching behavior
        Match m = c.Match(S);

        // Use member function on 'm'
        // find to check if string X
        // is present in S or not
        if (m.Success) {
            Console.WriteLine("Yes");
        }
        else {
            Console.WriteLine("No");
        }

        // Count the number of matches
        int numberOfMatches = 0;

        m = c.Match(S);

        while (m.Success) {
            numberOfMatches++;
            m = m.NextMatch();
        }

        // Print the count of occurrence
        Console.WriteLine("Frequency of string " + pattern
                           + " is " + numberOfMatches);
    }

    // Driver code
    public static void Main(string[] args)
    {
        // Given string str and pattern
        string str = "geeksforgeeks";
        string pattern = "geeks";

        // Function Call
        find_frequency(str, pattern);
    }
}


// This code is contribute by rishab

// JavaScript program for the above approach

function find_frequency(S, pattern) {
    // Create a regular expression
    // of the string pattern
    const c = new RegExp(pattern);
    
    // Determines the matching behavior
    const m = S.match(c);
    
    // Use member function on 'm'
    // find to check if string X
    // is present in S or not
    if (m !== null) {
        console.log("Yes");
    }
    else {
        console.log("No");
    }
    
    // Count the number of matches
    let numberOfMatches = 0;
    
    let m2 = c.exec(S);
    
    while (m2 != null)
    {
        numberOfMatches++;
        S = S.substr(m2.index + 1);
        m2 = c.exec(S);
    }
    
    // Print the count of occurrence
    console.log("Frequency of string " + pattern
        + " is " + numberOfMatches);

}

// Driver code
const str = "geeksforgeeks";
const pattern = "geeks";

// Function Call
find_frequency(str, pattern);


// This code is contribute by phasing17

Yes
Frequency of string geeks is 2

Time Complexity: O(N + M)
Auxiliary Space: O(M)