Related Articles

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

• Difficulty Level : Easy
• Last Updated : 28 May, 2021

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 :
After repeating given string 3 time, string becomes 100001100001100001.
The longest substring of 0’s is 4
Input : S = “010001000”, K = 4
Output : 4

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`

## Javascript

 ``

Output:

`4`

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

My Personal Notes arrow_drop_up