Find all the patterns of "1(0+)1" in a given string (General Approach)

Last Updated : 28 Jan, 2023

A string contains patterns of the form 1(0+)1 where (0+) represents any non-empty consecutive sequence of 0's. Count all such patterns. The patterns are allowed to overlap.

Note : It contains digits and lowercase characters only. The string is not necessarily a binary. 100201 is not a valid pattern.
One approach to solve the problem is discussed here, other using Regular expressions is given in Set 2

Examples:

Input : 1101001
Output : 2

Input : 100001abc101
Output : 2

Let size of input string be n.

Iterate through index '0' to 'n-1'.
If we encounter a '1', we iterate till the elements are '0'.
After the stream of zeros ends, we check whether we encounter a '1' or not.
Keep on doing this till we reach the end of string.

Below is the implementation of the above method.

Java

// Java Code to count 1(0+)1 
// patterns in a string 
import java.io.*;

class GFG 
{
    // Function to count patterns 
    static int patternCount(String str)
    {
        /* Variable to store the last character*/
        char last = str.charAt(0);
    
        int i = 1, counter = 0;
        while (i < str.length())
        {
            /* We found 0 and last character was '1',
            state change*/
            if (str.charAt(i) == '0' && last == '1')
            {
                while (i < str.length() && str.charAt(i) == '0')
                    i++;
    
                // After the stream of 0's, we 
                // got a '1',counter incremented
                // Break in case of non zero terminating string.
                if (i == str.length()) {
                    break; 
                }
                if (str.charAt(i) == '1')
                    counter++;
            }
          
            if (i == str.length()) {
                break; 
            }
    
            /* Last character stored */
            last = str.charAt(i);
            i++;
        }
    
        return counter;
    }
    
    // Driver Code 
    public static void main (String[] args)
    {
        String str = "1001ab010abc01001";
        System.out.println(patternCount(str));
        
    }
}

// This code is contributed by vt_m.

C++

/* Code to count 1(0+)1 patterns in a string */
#include <bits/stdc++.h>
using namespace std;

/* Function to count patterns */
int patternCount(string str)
{
    /* Variable to store the last character*/
    char last = str[0];

    int i = 1, counter = 0;
    while (i < str.size())
    {
        /* We found 0 and last character was '1',
          state change*/
        if (str[i] == '0' && last == '1')
        {
            while (str[i] == '0')
                i++;

            /* After the stream of 0's, we got a '1',
               counter incremented*/
            if (str[i] == '1')
                counter++;
        }

        /* Last character stored */
        last = str[i];
        i++;
    }

    return counter;
}

/* Driver Code */
int main()
{
    string str = "1001ab010abc01001";
    cout << patternCount(str) << endl;
    return 0;
}

Python3

# Python3 code to count 1(0+)1 patterns in a 

# Function to count patterns 
def patternCount(str):
    
    # Variable to store the last character
    last = str[0]

    i = 1; counter = 0
    while (i < len(str)):
        
        # We found 0 and last character was '1',
        # state change
        if (str[i] == '0' and last == '1'):
            while (str[i] == '0'):
                i += 1
                
                # After the stream of 0's, we got a '1',
                # counter incremented
                if (str[i] == '1'): 
                    counter += 1
        
        # Last character stored 
        last = str[i]
        i += 1
    
    return counter


# Driver Code 
str = "1001ab010abc01001"
ans = patternCount(str)
print (ans)
    
# This code is contributed by saloni1297

// C# Code to count 1(0 + )1 
// patterns in a string 
using System;

class GFG 
{
    
    // Function to count patterns 
    static int patternCount(String str)
    {
        // Variable to store the 
        // last character
        char last = str[0];
    
        int i = 1, counter = 0;
        while (i < str.Length)
        {
            // We found 0 and last 
            // character was '1',
            // state change
            if (str[i] == '0' && last == '1')
            {
                while (str[i] == '0')
                    i++;
    
                // After the stream of 0's, we 
                // got a '1',counter incremented
                if (str[i] == '1')
                    counter++;
            }
    
            // Last character stored 
            last = str[i];
            i++;
        }
    
        return counter;
    }
    
    // Driver Code 
    public static void Main ()
    {
        String str = "1001ab010abc01001";
        Console.Write(patternCount(str));
        
    }
}

// This code is contributed by nitin mittal

PHP

<?php
// PHP Code to count 1(0+)1 patterns 
// in a string

// Function to count patterns
function patternCount($str)
{
    
    // Variable to store the 
    // last character
    $last = $str[0];

    $i = 1; 
    $counter = 0;
    while ($i < strlen($str))
    {
        
        // We found 0 and last character
        // was '1', state change
        if ($str[$i] == '0' && $last == '1')
        {
            while ($str[$i] == '0')
                $i++;

            // After the stream of 0's,
            // we got a '1', counter 
            // incremented
            if ($str[$i] == '1')
                $counter++;
        }

        /* Last character stored */
        $last = $str[$i];
        $i++;
    }

    return $counter;
}

    // Driver Code
    $str = "1001ab010abc01001";
    echo patternCount($str) ;

// This code is contributed by nitin mittal
?>

JavaScript

<script>

// javascript Code to count 1(0+)1 
// patterns in a string 

    // Function to count patterns 
    function patternCount(str)
    {
        /* Variable to store the last character*/
        var last = str.charAt(0);
    
        var i = 1, counter = 0;
        while (i < str.length)
        {
            /* We found 0 and last character was '1',
            state change*/
            if (str.charAt(i) == '0' && last == '1')
            {
                while (str.charAt(i) == '0')
                    i++;
    
                // After the stream of 0's, we 
                // got a '1',counter incremented
                if (str.charAt(i) == '1')
                    counter++;
            }
    
            /* Last character stored */
            last = str.charAt(i);
            i++;
        }
    
        return counter;
    }
    
    // Driver Code 
    var str = "1001ab010abc01001";
    document.write(patternCount(str));


// This code is contributed by 29AjayKumar 
</script>

Output

Time Complexity: O(n)
Auxiliary Space: O(1)

Introduction to Pattern Searching - Data Structure and Algorithm Tutorial

kartik

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Find all the patterns of "1(0+)1" in a given string (General Approach)

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