# 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 ``#include ``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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