Count of occurrences of a "1(0+)1" pattern in a string

Last Updated : 15 Jul, 2022

Given an alphanumeric string, find the number of times a pattern 1(0+)1 occurs in the given string. Here, (0+) signifies the presence of non empty sequence of consecutive 0's.

Examples:

Input : 1001010001 Output : 3 First sequence is in between 0th and 3rd index. Second sequence is in between 3rd and 5th index. Third sequence is in between 5th and 9th index. So total number of sequences comes out to be 3.  Input : 1001ab010abc01001 Output : 2 First sequence is in between 0th and 3rd index. Second valid sequence is in between 13th and 16th index. So total number of sequences comes out to  be 2.

The idea to solve this problem is to first find a '1' and keep moving forward in the string and check as mentioned below:

If any character other than '0' and '1' is obtained then it means pattern is not valid. So we go on in the search of next '1' from this index and repeat these steps again.
If a '1' is seen, then check for the presence of '0' at previous position to check the validity of sequence.

Below is the implementation of above idea:

C++

// C++ program to calculate number of times // the pattern occurred in given string #include<iostream> using namespace std;  // Returns count of occurrences of "1(0+)1" // int str. int countPattern(string str) {     int len = str.size();     bool oneSeen = 0;      int count = 0;  // Initialize result     for (int i = 0; i < len ; i++)     {          // Check if encountered '1' forms a valid         // pattern as specified         if (str[i] == '1' && oneSeen == 1)             if (str[i - 1] == '0')                 count++;          // if 1 encountered for first time         // set oneSeen to 1         if (str[i] == '1' && oneSeen == 0)            {             oneSeen = 1;             continue;            }         // Check if there is any other character         // other than '0' or '1'. If so then set         // oneSeen to 0 to search again for new         // pattern         if (str[i] != '0' && str[i] != '1')             oneSeen = 0;       }      return count; }  // Driver program to test above function int main() {     string str = "100001abc101";     cout << countPattern(str);     return 0; }

Java

//Java program to calculate number of times //the pattern occurred in given string public class GFG {     // Returns count of occurrences of "1(0+)1"     // int str.     static int countPattern(String str)     {         int len = str.length();         boolean oneSeen = false;                  int count = 0;  // Initialize result         for(int i = 0; i < len ; i++)         {             char getChar = str.charAt(i);                          // Check if encountered '1' forms a valid             // pattern as specified             if (getChar == '1' && oneSeen == true){                 if (str.charAt(i - 1) == '0')                     count++;             }              // if 1 encountered for first time             // set oneSeen to 1             if(getChar == '1' && oneSeen == false)                 oneSeen = true;                          // Check if there is any other character             // other than '0' or '1'. If so then set             // oneSeen to 0 to search again for new             // pattern             if(getChar != '0' && str.charAt(i) != '1')                 oneSeen = false;                       }         return count;     }      // Driver program to test above function     public static void main(String[] args)     {          String str = "100001abc101";          System.out.println(countPattern(str));     }  } // This code is contributed by Sumit Ghosh

Python3

# Python program to calculate number of times # the pattern occurred in given string  # Returns count of occurrences of "1(0+)1" def countPattern(s):     length = len(s)     oneSeen = False          count = 0   # Initialize result     for i in range(length):          # Check if encountered '1' forms a valid         # pattern as specified         if (s[i] == '1' and oneSeen):             if (s[i - 1] == '0'):                 count += 1          # if 1 encountered for first time         # set oneSeen to 1         if (s[i] == '1' and oneSeen == 0):             oneSeen = True           # Check if there is any other character         # other than '0' or '1'. If so then set         # oneSeen to 0 to search again for new         # pattern         if (s[i] != '0' and s[i] != '1'):             oneSeen = False          return count  # Driver code s = "100001abc101" print(countPattern(s))  # This code is contributed by Sachin Bisht

// C# program to calculate number // of times the pattern occurred  // in given string  using System;  class GFG { // Returns count of occurrences  // of "1(0+)1" int str.  public static int countPattern(string str) {     int len = str.Length;     bool oneSeen = false;      int count = 0; // Initialize result     for (int i = 0; i < len ; i++)     {         char getChar = str[i];          // Check if encountered '1' forms          // a valid pattern as specified          if (getChar == '1' &&                   oneSeen == true)         {             if (str[i - 1] == '0')             {                 count++;             }         }          // if 1 encountered for first         // time set oneSeen to 1          if (getChar == '1' &&              oneSeen == false)         {             oneSeen = true;         }          // Check if there is any other character          // other than '0' or '1'. If so then set          // oneSeen to 0 to search again for new          // pattern          if (getChar != '0' &&                   str[i] != '1')         {             oneSeen = false;         }       }     return count; }  // Driver Code public static void Main(string[] args) {     string str = "100001abc101";     Console.WriteLine(countPattern(str)); }  }  // This code is contributed  // by Shrikant13

PHP

<?php  // PHP program to calculate number of times // the pattern occurred in given string  // Returns count of occurrences  // of "1(0+)1"  function countPattern($str) {     $len = strlen($str);     $oneSeen = 0;      $count = 0; // Initialize result     for ($i = 0; $i < $len ; $i++)     {         // Check if encountered '1' forms a         // valid pattern as specified         if ($str[$i] == '1' && $oneSeen == 1)             if ($str[$i - 1] == '0')                 $count++;          // if 1 encountered for first          // time set oneSeen to 1         if ($str[$i] == '1' && $oneSeen == 0)             $oneSeen = 1;          // Check if there is any other character         // other than '0' or '1'. If so then set         // oneSeen to 0 to search again for new         // pattern         if ($str[$i] != '0' && $str[$i] != '1')             $oneSeen = 0;       }      return $count; }  // Driver Code $str = "100001abc101"; echo countPattern($str);  // This code is contributed  // by ChitraNayal ?>

JavaScript

<script> //Javascript program to calculate number of times //the pattern occurred in given string          // Returns count of occurrences of "1(0+)1"     // int str.     function countPattern(str)     {         let len = str.length;         let oneSeen = false;                    let count = 0;  // Initialize result         for(let i = 0; i < len ; i++)         {             let getChar = str[i];                            // Check if encountered '1' forms a valid             // pattern as specified             if (getChar == '1' && oneSeen == true){                 if (str[i-1] == '0')                     count++;             }                // if 1 encountered for first time             // set oneSeen to 1             if(getChar == '1' && oneSeen == false)                 oneSeen = true;                            // Check if there is any other character             // other than '0' or '1'. If so then set             // oneSeen to 0 to search again for new             // pattern             if(getChar != '0' && str[i] != '1')                 oneSeen = false;                           }         return count;     }          // Driver program to test above function     let str = "100001abc101";     document.write(countPattern(str));          //This code is contributed by avanitrachhadiya2155      </script>

Output

Time Complexity: O( N ), where N is the length of input string.
Auxiliary Space: O(1), as extra space is not required

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

Sakshi Tiwari

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Count of occurrences of a "1(0+)1" pattern in a string

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