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Check three or more consecutive identical characters or numbers
  • Last Updated : 01 Feb, 2021

Given string str, the task is to check whether the given string contains 3 or more consecutive identical characters/numbers or not by using Regular Expression
Examples: 

Input: str = “aaa”; 
Output: true 
Explanation: 
The given string contains a, a, a which are consecutive identical characters.
Input: str = “abc”; 
Output: false 
Explanation: 
The given string contains a, b, c which are not consecutive identical characters.
Input: str = “11”; 
Output: false 
Explanation: 
The given string contains 1, 1 which are not 3 or more consecutive identical numbers. 

Approach: The idea is to use Regular Expression to solve this problem. The following steps can be followed to compute the answer. 

  • Get the String.
  • Create a regular expression to check 3 or more consecutive identical characters or numbers as mentioned below: 
     

regex = “\\b([a-zA-Z0-9])\\1\\1+\\b”; 
 

  • Where: 
    • \\b represents the word boundary.
    • ( represents the starting of the group 1.
    • [a-zA-Z0-9] represents a letter or a digit.
    • ) represents the ending of the group 1.
    • \\1 represents the same character as group 1.
    • \\1+ represents the same character as group 1 one or more times.
    • \\b represents the word boundary.
  1. Match the given string with the Regular Expression. In Java, this can be done by using Pattern.matcher().
  2. Return true if the string matches with the given regular expression, else return false.

Below is the implementation of the above approach:
 

C++




// C++ program to check
// three or more consecutive identical
// characters or numbers using Regular Expression
#include <iostream>
#include <regex>
using namespace std;
 
// Function to check three or more
// consecutive identical characters or numbers.
bool isIdentical(string str)
{
 
  // Regex to check valid three or more
  // consecutive identical characters or numbers.
  const regex pattern("\\b([a-zA-Z0-9])\\1\\1+\\b");
 
 
  // If the three or more consecutive
  // identical characters or numbers
  // is empty return false
  if (str.empty())
  {
     return false;
  }
 
  // Return true if the three or more
  // consecutive identical characters or numbers
  // matched the ReGex
  if(regex_match(str, pattern))
  {
    return true;
  }
  else
  {
    return false;
  }
}
 
// Driver Code
int main()
{
   
  // Test Case 1:
  string str1 = "aaa";
  cout << isIdentical(str1) << endl;
 
  // Test Case 2:
  string str2 = "11111";
  cout << isIdentical(str2) << endl;
 
  // Test Case 3:
  string str3 = "aaab";
  cout << isIdentical(str3) << endl;
 
  // Test Case 4:
  string str4 = "abc";
  cout << isIdentical(str4) << endl;
 
  // Test Case 5:
  string str5 = "aa";
  cout << isIdentical(str5) << endl;
  return 0;
}
 
// This code is contributed by yuvraj_chandra

Java




// Java program to check three or
// more consecutive identical
// characters or numbers
// using regular expression
 
import java.util.regex.*;
class GFG {
 
    // Function to check three or
    // more consecutive identical
    // characters or numbers
    // using regular expression
    public static boolean isIdentical(String str)
    {
        // Regex to check three or
        // more consecutive identical
        // characters or numbers
        String regex
            = "\\b([a-zA-Z0-9])\\1\\1+\\b";
 
        // Compile the ReGex
        Pattern p
            = Pattern.compile(regex);
 
        // If the string is empty
        // return false
        if (str == null) {
            return false;
        }
 
        // Find match between given string
        // and regular expression
        // using Pattern.matcher()
        Matcher m = p.matcher(str);
 
        // Return if the string
        // matched the ReGex
        return m.matches();
    }
 
    // Driver code
    public static void main(String args[])
    {
 
        // Test Case 1:
        String str1 = "aaa";
        System.out.println(
            isIdentical(str1));
 
        // Test Case 2:
        String str2 = "11111";
        System.out.println(
            isIdentical(str2));
 
        // Test Case 3:
        String str3 = "aaab";
        System.out.println(
            isIdentical(str3));
 
        // Test Case 4:
        String str4 = "abc";
        System.out.println(
            isIdentical(str4));
 
        // Test Case 5:
        String str5 = "aa";
        System.out.println(
            isIdentical(str5));
    }
}

Python3




# Python3 program to check three or
# more consecutiveidentical
# characters or numbers
# using regular expression
import re
 
# Function to check three or
# more consecutiveidentical
# characters or numbers
# using regular expression
def isValidGUID(str):
 
    # Regex to check three or
    # more consecutive identical
    # characters or numbers
    regex = "\\b([a-zA-Z0-9])\\1\\1+\\b"
     
    # Compile the ReGex
    p = re.compile(regex)
 
    # If the string is empty
    # return false
    if (str == None):
        return False
 
    # Return if the string
    # matched the ReGex
    if(re.search(p, str)):
        return True
    else:
        return False
 
# Driver code
 
# Test Case 1:
str1 = "aaa"
print(isValidGUID(str1))
 
# Test Case 2:
str2 = "11111"
print(isValidGUID(str2))
 
# Test Case 3:
str3 = "aaab"
print(isValidGUID(str3))
 
# Test Case 4:
str4 = "abc"
print(isValidGUID(str4))
 
# Test Case 4:
str5 = "aa"
print(isValidGUID(str5))
 
# This code is contributed by avanitrachhadiya2155
Output: 
true
true
false
false
false

 




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