Given a binary string **S**, and a substring **K**, the task is to find the minimum no of steps required to flip the characters in a binary string such that it doesn’t contain the given substring **K**. **Note:** In one step we can change 0 to 1 or vice versa.**Examples:**

Input:S = “0111011”, K = “011”Output:2Explanation:

In the above string we have the substring 011 for 2 times, hence change the 3rd bit and 7th bit.

Input:S = “010010”, K = “0100”Output:1Explanation:

In the above string we have the substring 0100 for 1 time, change the 4th bit of the string to 1.

**Naive Approach:** The naive approach is to use the Pattern Searching. Iterate through the string for **N! times**(N = length of the binary string). In every iteration check for the substring **K** and if its a match then increment the count. At last, print the count which will be the number of steps required to make the string such that it doesn’t contain the given substring **K**.

**Time Complexity:** *O(M*N)* where **M** is the length of substring and **N** is the length of the binary string. **Auxiliary Space:** *O(1)*

**Efficient Approach:** To optimize the above method, the idea is to **replace the substring with an empty string** and subtract the resultant string length from original string length. After this divide the resultant string with the length of the given substring **K** to get the minimum no of steps required to flip the characters of the given string **S** so that it doesn’t contain the given substring **K**.

Below is the implementation of the above approach:

## C++

`// C++ program for the above approach` `#include<bits/stdc++.h>` `#include <boost/algorithm/string/replace.hpp>` `using` `namespace` `std;` `// Function that counts the total` `// number of character to be flipped` `// such the string b doesn't contains` `// string sub as a substring` `int` `flipCharacters(string b,` ` ` `string sub)` `{` ` ` ` ` `// Replacing the substring with ""` ` ` `// and find the difference between` ` ` `// the length of the resultant` ` ` `// string and the original` ` ` `// string length` ` ` `int` `res = b.size();` ` ` `boost::replace_all(b, sub, ` `""` `);` ` ` `res = res - b.size();` ` ` ` ` `// Divide the result` ` ` `// with substring length` ` ` `int` `temp = res / sub.size();` ` ` `// Return the final count` ` ` `return` `temp;` `}` `// Driver Code` `int` `main()` `{` ` ` ` ` `// Given string S and substring K` ` ` `string S = ` `"010010"` `;` ` ` `string K = ` `"0100"` `;` ` ` `// Function call` ` ` `int` `result = flipCharacters(S, K);` ` ` `// Print the minimum flip` ` ` `cout << (result);` `}` `// This code is contributed by Amit Katiyar` |

## Java

`// Java program for the above approach` `import` `java.util.*;` `public` `class` `Test {` ` ` `// Function that counts the total` ` ` `// number of character to be flipped` ` ` `// such the string b doesn't contains` ` ` `// string sub as a substring` ` ` `static` `int` `flipCharacters(String b,` ` ` `String sub)` ` ` `{` ` ` `// Replacing the substring with ""` ` ` `// and find the difference between` ` ` `// the length of the resultant` ` ` `// string and the original` ` ` `// string length` ` ` `int` `res = b.length()` ` ` `- b.replaceAll(sub, ` `""` `)` ` ` `.length();` ` ` `// Divide the result` ` ` `// with substring length` ` ` `int` `temp = res / sub.length();` ` ` `// Return the final count` ` ` `return` `temp;` ` ` `}` ` ` `// Driver Code` ` ` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `// Given string S and substring K` ` ` `String S = ` `"010010"` `;` ` ` `String K = ` `"0100"` `;` ` ` `// Function Call` ` ` `int` `result = flipCharacters(S, K);` ` ` `// Print the minimum flip` ` ` `System.out.println(result);` ` ` `}` `}` |

## Python3

`# Python3 program for the above approach` `def` `flipCharacters(b, sub):` ` ` ` ` `# Replace the substring with` ` ` `# "" (emptryString)` ` ` `b1 ` `=` `b.replace(sub, "")` ` ` ` ` `n ` `=` `int` `((` `len` `(b)` `-` `len` `(b1))` `/` `len` `(sub))` ` ` ` ` `return` `n` `# Driver Code` `if` `__name__ ` `=` `=` `'__main__'` `:` `# Given string S and substring K` ` ` `S ` `=` `"010010"` ` ` `X ` `=` `"0100"` `# Function Call` ` ` `result ` `=` `flipCharacters(S, X)` `# Print the minimum flip` ` ` `print` `(result)` |

## C#

`// C# program for the above approach` `using` `System;` `class` `GFG` `{` ` ` ` ` `// Function that counts the total` ` ` `// number of character to be flipped` ` ` `// such the string b doesn't contains` ` ` `// string sub as a substring` ` ` `static` `int` `flipCharacters(` `string` `b,` ` ` `string` `sub)` ` ` `{` ` ` `// Replacing the substring with ""` ` ` `// and find the difference between` ` ` `// the length of the resultant` ` ` `// string and the original` ` ` `// string length` ` ` `int` `res = b.Length -` ` ` `b.Replace(sub, ` `""` `).Length;` ` ` `// Divide the result` ` ` `// with substring length` ` ` `int` `temp = res / sub.Length;` ` ` `// Return the final count` ` ` `return` `temp;` ` ` `}` ` ` `// Driver Code` ` ` `public` `static` `void` `Main(` `string` `[] args)` ` ` `{` ` ` `// Given string S and substring K` ` ` `string` `S = ` `"010010"` `;` ` ` `string` `K = ` `"0100"` `;` ` ` `// Function Call` ` ` `int` `result = flipCharacters(S, K);` ` ` `// Print the minimum flip` ` ` `Console.Write(result);` ` ` `}` `}` `// This code is contributed by rutvik_56` |

**Output:**

1

**Time Complexity:** *O(N)*, where N is the length of the string. **Auxiliary Space:** *O(1)*