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#

// 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)

Suggest improvement

Count of number of given string in 2D character array

Maximum length prefix of one string that occurs as subsequence in another

Share your thoughts in the comments

Suffix Tree construction

Suffix Tree Application

More practice problems on pattern searching algorithms