Maximum length of consecutive 1s or 0s after flipping at most K characters

• Last Updated : 15 Nov, 2021

Given a binary string S of size N and an integer K, the task is to find the maximum length of consecutive 1s or 0s after flipping at most K characters of the given binary string S.

Examples

Input: S = “1001”, K = 1
Output: 3
Explanation:
Flip the K(= 1) characters at index 3 of the string modifies the string S to “1000”. Now the maximum length of consecutive 0s is 3, which is the required result.

Input: S = “11011011”, K = 3
Output: 8

Approach: The given problem can be solved using the Two Pointer Approach and Sliding Window approach. Follow the steps to solve the given problem:

• Initialize a function, say maxLength(S, N, ch, K) that find the maximum length of characters ch after flipping at most K characters using the following steps:
1. Initialize a variable, say cnt that stores the count of character ch in the window.
2. Initialize a variable, say left that stores the starting of the resultant window.
3. Initialize a variable, say ans that stores the resultant length of consecutive K characters as ch after at most K flips.
4. Traverse the string S using the variable right and perform the following steps:
• If the value of S[right] is ch, then increment the value of cnt by 1.
• Iterate until the value of cnt is greater than K, then increment the left pointer and decrement the value of cnt by 1.
• Update the value of ans to maximum of ans and (right – left + 1).
• After completing the above steps, print the maximum of the value returned by the maxLength(S, N, ‘0’, K) and maxLength(S, N, ‘1’, K) as the result.

Below is the implementation of the above approach:

C++

 // C++ program for the above approach #include using namespace std;   // Function to find the maximum length // continuous segment of character c after // flipping at most K characters int maxLength(string str, int n,               char c, int k) {     // Stores the maximum length     int ans = -1;       // Stores the count of char 'c'     int cnt = 0;       // Start of window     int left = 0;       for (int right = 0; right < n; right++) {           if (str[right] == c) {             cnt++;         }           // Remove the extra 'c' from left         while (cnt > k) {             if (str[left] == c) {                 cnt--;             }               // Increment the value of             // the left             left++;         }           // Update the resultant maximum         // length of character ch         ans = max(ans, right - left + 1);     }       return ans; }   // Function to find the maximum length // of consecutive 0s or 1s by flipping // at most K characters of the string int maxConsecutiveSegment(string S, int K) {     int N = S.length();       // Print the maximum of the maximum     // length of 0s or 1s     return max(maxLength(S, N, '0', K),                maxLength(S, N, '1', K)); }   // Driver Code int main() {     string S = "1001";     int K = 1;     cout << maxConsecutiveSegment(S, K);       return 0; }

Java

 // Java program for the above approach public class GFG {           // Function to find the maximum length     // continuous segment of character c after     // flipping at most K characters     static int maxLength(String str, int n,                   char c, int k)     {                 // Stores the maximum length         int ans = -1;               // Stores the count of char 'c'         int cnt = 0;               // Start of window         int left = 0;               for (int right = 0; right < n; right++) {                   if (str.charAt(right) == c) {                 cnt++;             }                   // Remove the extra 'c' from left             while (cnt > k) {                 if (str.charAt(left) == c) {                     cnt--;                 }                       // Increment the value of                 // the left                 left++;             }                   // Update the resultant maximum             // length of character ch             ans = Math.max(ans, right - left + 1);         }               return ans;     }           // Function to find the maximum length     // of consecutive 0s or 1s by flipping     // at most K characters of the string     static int maxConsecutiveSegment(String S, int K)     {         int N = S.length();               // Print the maximum of the maximum         // length of 0s or 1s         return Math.max(maxLength(S, N, '0', K),                    maxLength(S, N, '1', K));     }           // Driver Code     int main()     {                 return 0;     }       // Driver code     public static void main (String[] args) {                   String S = "1001";         int K = 1;         System.out.println(maxConsecutiveSegment(S, K));               } }   // This code is contributed by AnkThon

Python3

 # python program for the above approach   # Function to find the maximum length # continuous segment of character c after # flipping at most K characters def maxLength(str, n, c, k):       # Stores the maximum length     ans = -1       # Stores the count of char 'c'     cnt = 0       # Start of window     left = 0       for right in range(0, n):           if (str[right] == c):             cnt += 1           # Remove the extra 'c' from left         while (cnt > k):             if (str[left] == c):                 cnt -= 1               # Increment the value of             # the left             left += 1           # Update the resultant maximum         # length of character ch         ans = max(ans, right - left + 1)       return ans     # Function to find the maximum length # of consecutive 0s or 1s by flipping # at most K characters of the string def maxConsecutiveSegment(S,  K):       N = len(S)       # Print the maximum of the maximum     # length of 0s or 1s     return max(maxLength(S, N, '0', K), maxLength(S, N, '1', K))     # Driver Code if __name__ == "__main__":       S = "1001"     K = 1     print(maxConsecutiveSegment(S, K))   # This code is contributed by rakeshsahni

C#

 // C# program for the above approach using System; public class GFG {       // Function to find the maximum length     // continuous segment of character c after     // flipping at most K characters     static int maxLength(String str, int n,                   char c, int k)     {           // Stores the maximum length         int ans = -1;           // Stores the count of char 'c'         int cnt = 0;           // Start of window         int left = 0;           for (int right = 0; right < n; right++)         {               if (str[right] == c)             {                 cnt++;             }               // Remove the extra 'c' from left             while (cnt > k)             {                 if (str[left] == c)                 {                     cnt--;                 }                   // Increment the value of                 // the left                 left++;             }               // Update the resultant maximum             // length of character ch             ans = Math.Max(ans, right - left + 1);         }           return ans;     }       // Function to find the maximum length     // of consecutive 0s or 1s by flipping     // at most K characters of the string     static int maxConsecutiveSegment(String S, int K)     {         int N = S.Length;           // Print the maximum of the maximum         // length of 0s or 1s         return Math.Max(maxLength(S, N, '0', K),                    maxLength(S, N, '1', K));     }         // Driver code     public static void Main()     {           String S = "1001";         int K = 1;         Console.WriteLine(maxConsecutiveSegment(S, K));       } }   // This code is contributed by Saurabh Jaiswal

Javascript



Output:

3

Time Complexity: O(N)
Auxiliary Space: O(1)

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