# Longest sub string of 0’s in a binary string which is repeated K times

Given binary string S of size N and a number K. The task is to find the Longest sub string of 0’s in the string which is formed by repeating given string K times.

Examples:

Input : S = “100001” , K = 3
Output : 4
After repeating given string 3 time, string becomes 100001100001100001.
The longest substring of 0’s is 4

Input : S = “010001000”, K = 4
Output : 4

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

1. If K is one, then find the longest substring of 0’s in a string using a simple loops
2. If K is greater than one, then add a given string to the end of the string. Then string becomes S+S and length will be 2*N and find the longest substring of 0’s in a string using a simple loops
• If the longest substring is 2*N then, our answer will be K*N
• Otherwise it will be the our required answer

Below is the implementation of the above approach:

## C++

 `// C++ program to find the find the Longest continuous ` `// sequence of '0' after repeating Given string K time ` `#include ` `using` `namespace` `std; ` ` `  `// Function to find the longest substring of 0's ` `int` `longest_substring(string s, ``int` `k) ` `{ ` `    ``// To store size of the string ` `    ``int` `n = s.size(); ` `     `  `    ``if``(k>1) ` `    ``{ ` `        ``s += s; ` `        ``n *= 2; ` `    ``}     ` `     `  `    ``// To store the required answer ` `    ``int` `ans = 0; ` `     `  `    ``// Find the longest substring of 0's ` `    ``int` `i = 0; ` `    ``while` `(i < n) ` `    ``{ ` `        ``int` `x = 0; ` `         `  `        ``// Run a loop upto s[i] is zero ` `        ``while` `(s[i] == ``'0'` `&& i < n) ` `            ``x++, i++; ` `        ``ans = max(ans, x); ` `        ``i++; ` `    ``} ` `     `  `    ``// Check the conditions ` `    ``if``(k==1 or ans!=n) ` `        ``return` `ans; ` `         `  `    ``else` `        ``return` `(ans/2)*k; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string s = ``"010001000"``; ` `     `  `    ``int` `k = 4; ` `     `  `    ``// Function call ` `    ``cout << longest_substring(s, k); ` `     `  `    ``return` `0; ` `} `

## Java

 `// Java program to find the Longest continuous ` `// sequence of '0' after repeating Given string K time ` `class` `GFG ` `{ ` ` `  `// Function to find the longest substring of 0's ` `static` `int` `longest_substring(String s, ``int` `k) ` `{ ` `    ``// To store size of the string ` `    ``int` `n = s.length(); ` `     `  `    ``if``(k > ``1``) ` `    ``{ ` `        ``s += s; ` `        ``n *= ``2``; ` `    ``}  ` `     `  `    ``// To store the required answer ` `    ``int` `ans = ``0``; ` `     `  `    ``// Find the longest substring of 0's ` `    ``int` `i = ``0``; ` `    ``while` `(i < n) ` `    ``{ ` `        ``int` `x = ``0``; ` `         `  `        ``// Run a loop upto s[i] is zero ` `        ``while` `(i < n && s.charAt(i) == ``'0'``) ` `        ``{ ` `            ``x++; i++; ` `        ``} ` `        ``ans = Math.max(ans, x); ` `        ``i++; ` `    ``} ` `     `  `    ``// Check the conditions ` `    ``if``(k == ``1` `|| ans != n) ` `        ``return` `ans; ` `         `  `    ``else` `        ``return` `(ans / ``2``) * k; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``String s = ``"010001000"``; ` `     `  `    ``int` `k = ``4``; ` `     `  `    ``// Function call ` `    ``System.out.println(longest_substring(s, k)); ` `} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

## Python3

 `# Python3 program to find the find the Longest continuous ` `# sequence of '0' after repeating Given K time ` ` `  `# Function to find the longest subof 0's ` `def` `longest_substring(s, k): ` `    ``# To store size of the string ` `    ``n ``=` `len``(s) ` ` `  `    ``if``(k>``1``): ` `        ``s ``+``=` `s ` `        ``n ``*``=` `2` ` `  `    ``# To store the required answer ` `    ``ans ``=` `0` ` `  `    ``# Find the longest subof 0's ` `    ``i ``=` `0` `    ``while` `(i < n): ` `        ``x ``=` `0` ` `  `        ``# Run a loop upto s[i] is zero ` `        ``while` `(i < n ``and` `s[i] ``=``=` `'0'``): ` `            ``x,i``=``x``+``1``, i``+``1` `        ``ans ``=` `max``(ans, x) ` `        ``i``+``=``1` ` `  `    ``# Check the conditions ` `    ``if``(k``=``=``1` `or` `ans!``=``n): ` `        ``return` `ans ` ` `  `    ``else``: ` `        ``return` `(ans``/``/``2``)``*``k ` ` `  ` `  `# Driver code ` ` `  `s ``=` `"010001000"` ` `  `k ``=` `4` ` `  `# Function call ` `print``(longest_substring(s, k)) ` ` `  `# This code is contributed by mohit kumar 29 `

## C#

 `// C# program to find the Longest continuous ` `// sequence of '0' after repeating Given string K time ` `using` `System; ` `     `  `class` `GFG ` `{ ` ` `  `// Function to find the longest substring of 0's ` `static` `int` `longest_substring(String s, ``int` `k) ` `{ ` `    ``// To store size of the string ` `    ``int` `n = s.Length; ` `     `  `    ``if``(k > 1) ` `    ``{ ` `        ``s += s; ` `        ``n *= 2; ` `    ``}  ` `     `  `    ``// To store the required answer ` `    ``int` `ans = 0; ` `     `  `    ``// Find the longest substring of 0's ` `    ``int` `i = 0; ` `    ``while` `(i < n) ` `    ``{ ` `        ``int` `x = 0; ` `         `  `        ``// Run a loop upto s[i] is zero ` `        ``while` `(i < n && s[i] == ``'0'``) ` `        ``{ ` `            ``x++; i++; ` `        ``} ` `        ``ans = Math.Max(ans, x); ` `        ``i++; ` `    ``} ` `     `  `    ``// Check the conditions ` `    ``if``(k == 1 || ans != n) ` `        ``return` `ans; ` `         `  `    ``else` `        ``return` `(ans / 2) * k; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args)  ` `{ ` `    ``String s = ``"010001000"``; ` `     `  `    ``int` `k = 4; ` `     `  `    ``// Function call ` `    ``Console.WriteLine(longest_substring(s, k)); ` `} ` `} ` ` `  `// This code is contributed by PrinciRaj1992  `

Output:

```4
```

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :
Practice Tags :

1

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.