Count occurrences of a word in string | Set 2 (Using Regular Expressions)

Given a string str and a word w, the task is to print the number of the occurrence of the given word in the string str using Regular Expression.

Examples:

Input: str = "peter parker picked a peck of pickled peppers”, w = "peck"
Output: 1
Explanation: There is only one occurrence of the word "peck" in the given string. Therefore, the output is 1.

Input: str = "How much wood would a woodchuck chuck if a woodchuck could chuck wood ?", w = "wood"
Output: 2
Explanation: There are only two occurrences of the word "wood" in the given string. 
Therefore, the output is 2.

Input: str = "She sells seashells by the seashore", w = "sea"
Output: 0
Explanation: There is no occurrence of the word "sea" in the given string. Therefore, the output is 0.

Approach: The required regular expression to find the required count of string w in the given string is "\\bw\\b", where \b is a word boundary. Follow the steps to solve the problem

• Create the regular expression pattern for the word w

regex = "\\bw\\b"

• Traverse the string, match the regex with the string str using regex_iterator(). Simultaneously, update number of matches. 
• Print the total number of matches obtained in the above step.

Below is the implementation of the above approach :

// C++ program for the above approach
#include <iostream>
#include <regex>
using namespace std;

// Function to count total occurrences
// of word "w" in string "str"
void countOccurrences(string str, string w)
{
    // Get the regex to be checked
    string regexPattern = "\\b" + w + "\\b";
    const regex pattern(regexPattern);

    // Variable to count total
    // occurrences of the given word
    int count = 0;

    auto it
        = sregex_iterator(str.begin(), str.end(), pattern);

    for (it; it != sregex_iterator(); it++) {

        // Increment count
        count++;
    }

    // Print the occurrences of the word
    cout << count << endl;

    return;
}

// Driver Code
int main()
{
    // Input
    string str
        = "peter parker picked a peck of pickled peppers";
    string w = "peck";

    countOccurrences(str, w);

    return 0;
}

// Java program for the above approach
import java.util.*;
import java.util.regex.*;

class GFG {

  // Function to count total occurrences
  // of word "w" in String "str"
  static void countOccurrences(String str, String w) 
  {
    
    // Get the regex to be checked
    String regexPattern = "\\b" + w + "\\b";

    Pattern pattern = Pattern.compile(regexPattern);
    
    // Variable to count total
    // occurrences of the given word
    int count = 0;

    while (str.contains(w)) {
      str = str.replace(w, "");
      // Increment count
      count++;
    }

    // Print the occurrences of the word
    System.out.print(count + "\n");

    return;
  }

  // Driver Code
  public static void main(String[] args)
  {
    
    // Input
    String str = "peter parker picked a peck of pickled peppers";
    String w = "peck";

    countOccurrences(str, w);
  }
}

// This code is contributed by gauravrajput1 

# Python program for the above approach
import re

# Function to count total occurrences
# of word "w" in String "str"
def countOccurrences(str,w):
    # Get the regex to be checked
    regexPattern = "\\b" + w + "\\b"
    
    # Variable to count total
    # occurrences of the given word
    count=0
    
    for m in re.finditer(regexPattern, str):
        # Increment count
        count=count+1
        
    # Print the occurrences of the word
    print(count)
    
# Driver Code

# Input
str = "peter parker picked a peck of pickled peppers"
w = "peck"
countOccurrences(str,w)

# This code is contributed by Pushpesh Raj.

// C# program for the above approach
using System;
using System.Text.RegularExpressions;
public class GFG {

  // Function to count total occurrences
  // of word "w" in String "str"
  static void countOccurrences(String str, String w) 
  {

    // Get the regex to be checked
    String regexPattern = "\\b" + w + "\\b";

    Regex rx = new Regex(regexPattern,RegexOptions.Compiled | RegexOptions.IgnoreCase);
    // Variable to count total
    // occurrences of the given word
    int count = 0;

    while (str.Contains(w)) {
      str = str.Replace(w, "");
      // Increment count
      count++;
    }

    // Print the occurrences of the word
    Console.Write(count + "\n");

    return;
  }

  // Driver Code
  public static void Main(String[] args)
  {

    // Input
    String str = "peter parker picked a peck of pickled peppers";
    String w = "peck";

    countOccurrences(str, w);
  }
}

// This code is contributed by gauravrajput1

//// Javascript program for the above approach
function countOccurrences(string, substring) {
  var n = 0;
  var position = 0;
  while (true) {
    position = string.indexOf(substring, position);
    if (position != -1) {
      n++;
      position += substring.length;
    } else {
      break;
    }
  }
  return n;
}
console.log(countOccurrences("peter parker picked a peck of pickled peppers", "peck")); 
// This code is contributed By Rahul Chauhan

1

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