Given a binary strings **S** of length **N**, the task is to obtain **S** from a string, say **T**, of length **N** consisting only of zeroes, by minimum number of operations. Each operation involves choosing any index **i** from string **S** and flipping all the bits at indices **[i, N – 1]** of the string **T**. **Examples:**

Input:S = “101”Output:3Explanation:

“000” -> “111” -> “100” -> “101”.

Therefore, the minimum number of steps required is 3.Input:S = “10111”Output:3Explanation:

“00000” -> “11111” -> “10000” -> “10111”.

Therefore, the minimum number of steps required is 3.

**Approach:**

The idea is to find the first occurrence of **1** in the given string **S** and perform the given operation at that index. After this step, for every mismatch in the character of **S** and **T** at a particular index, repeat the opertion.

Follow the steps below:

- Iterate over
**S**and mark the first occurrence of**1**. - Initialize two variables, say
and**last**, where**ans****last**stores the character (**0 or 1**) for which the last operation was performed and**ans**keeps count of the minimum number of steps required. - Iterate from the first occurrence of
**1**till the end of the string. - If the current character is
**0**and**last = 1**, then increment the count of, and set**ans****last = 0**. - Otherwise, if
**last = 0**and the current character is**1**, then set**last = 1**. - Return the final value of
**ans**.

Below is the implementation of the above approach:

## C++

`// C++ Program to implement` `// the above approach` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to find the minimum` `// number of operations required` `// to obtain the string s` `int` `minOperations(string s)` `{` ` ` `int` `n = s.size();` ` ` `int` `pos = -1;` ` ` `// Iterate the string s` ` ` `for` `(` `int` `i = 0; i < s.size(); i++) {` ` ` `// If first occurrence of 1` ` ` `// is found` ` ` `if` `(s[i] == ` `'1'` `) {` ` ` `// Mark the index` ` ` `pos = i;` ` ` `break` `;` ` ` `}` ` ` `}` ` ` `// Base case: If no 1 occurred` ` ` `if` `(pos == -1) {` ` ` `// No operations required` ` ` `return` `0;` ` ` `}` ` ` `// Stores the character` ` ` `// for which last operation` ` ` `// was performed` ` ` `int` `last = 1;` ` ` `// Stores minimum number` ` ` `// of operations` ` ` `int` `ans = 1;` ` ` `// Iterate from pos to n` ` ` `for` `(` `int` `i = pos + 1; i < n; i++) {` ` ` `// Check if s[i] is 0` ` ` `if` `(s[i] == ` `'0'` `) {` ` ` `// Check if last operation was` ` ` `// performed because of 1` ` ` `if` `(last == 1) {` ` ` `ans++;` ` ` `// Set last to 0` ` ` `last = 0;` ` ` `}` ` ` `}` ` ` `else` `{` ` ` `if` `(last == 0) {` ` ` `// Check if last operation was` ` ` `// performed because of 0` ` ` `ans++;` ` ` `// Set last to 1` ` ` `last = 1;` ` ` `}` ` ` `}` ` ` `}` ` ` `// Return the answer` ` ` `return` `ans;` `}` `// Driver Code` `int` `main()` `{` ` ` `string s = ` `"10111"` `;` ` ` `cout << minOperations(s);` ` ` `return` `0;` `}` |

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## Java

`// Java program to implement the` `// above approach` `import` `java.util.*;` `class` `GFG{` `// Function to find the minimum` `// number of operations required` `// to obtain the string s` `static` `int` `minOperations(String s)` `{` ` ` `int` `n = s.length();` ` ` `int` `pos = -` `1` `;` ` ` `// Iterate the string s` ` ` `for` `(` `int` `i = ` `0` `; i < s.length(); i++) ` ` ` `{` ` ` ` ` `// If first occurrence of 1` ` ` `// is found` ` ` `if` `(s.charAt(i) == ` `'1'` `)` ` ` `{` ` ` ` ` `// Mark the index` ` ` `pos = i;` ` ` `break` `;` ` ` `}` ` ` `}` ` ` `// Base case: If no 1 occurred` ` ` `if` `(pos == -` `1` `)` ` ` `{` ` ` `// No operations required` ` ` `return` `0` `;` ` ` `}` ` ` `// Stores the character` ` ` `// for which last operation` ` ` `// was performed` ` ` `int` `last = ` `1` `;` ` ` `// Stores minimum number` ` ` `// of operations` ` ` `int` `ans = ` `1` `;` ` ` `// Iterate from pos to n` ` ` `for` `(` `int` `i = pos + ` `1` `; i < n; i++)` ` ` `{` ` ` ` ` `// Check if s[i] is 0` ` ` `if` `(s.charAt(i) == ` `'0'` `)` ` ` `{` ` ` `// Check if last operation was` ` ` `// performed because of 1` ` ` `if` `(last == ` `1` `) ` ` ` `{` ` ` `ans++;` ` ` `// Set last to 0` ` ` `last = ` `0` `;` ` ` `}` ` ` `}` ` ` `else` ` ` `{` ` ` `if` `(last == ` `0` `) ` ` ` `{` ` ` `// Check if last operation was` ` ` `// performed because of 0` ` ` `ans++;` ` ` `// Set last to 1` ` ` `last = ` `1` `;` ` ` `}` ` ` `}` ` ` `}` ` ` ` ` `// Return the answer` ` ` `return` `ans;` `}` `// Driver code` `public` `static` `void` `main(String[] args)` `{` ` ` `String s = ` `"10111"` `;` ` ` ` ` `System.out.println(minOperations(s));` `}` `}` `// This code is contributed by offbeat` |

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## Python3

`# Python3 program to implement` `# the above approach` `# Function to find the minimum` `# number of operations required` `# to obtain the string s` `def` `minOperations(s):` ` ` `n ` `=` `len` `(s)` ` ` `pos ` `=` `-` `1` ` ` `# Iterate the string s` ` ` `for` `i ` `in` `range` `(` `len` `(s)):` ` ` `# If first occurrence of 1` ` ` `# is found` ` ` `if` `(s[i] ` `=` `=` `'1'` `):` ` ` `# Mark the index` ` ` `pos ` `=` `i` ` ` `break` ` ` `# Base case: If no 1 occurred` ` ` `if` `(pos ` `=` `=` `-` `1` `):` ` ` `# No operations required` ` ` `return` `0` ` ` `# Stores the character` ` ` `# for which last operation` ` ` `# was performed` ` ` `last ` `=` `1` ` ` `# Stores minimum number` ` ` `# of operations` ` ` `ans ` `=` `1` ` ` `# Iterate from pos to n` ` ` `for` `i ` `in` `range` `(pos ` `+` `1` `, n):` ` ` `# Check if s[i] is 0` ` ` `if` `(s[i] ` `=` `=` `'0'` `):` ` ` `# Check if last operation was` ` ` `# performed because of 1` ` ` `if` `(last ` `=` `=` `1` `):` ` ` `ans ` `+` `=` `1` ` ` `# Set last to 0` ` ` `last ` `=` `0` ` ` ` ` `else` `:` ` ` `if` `(last ` `=` `=` `0` `):` ` ` `# Check if last operation was` ` ` `# performed because of 0` ` ` `ans ` `+` `=` `1` ` ` `# Set last to 1` ` ` `last ` `=` `1` ` ` `# Return the answer` ` ` `return` `ans` `# Driver Code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` ` ` `s ` `=` `"10111"` ` ` `print` `(minOperations(s))` `# This code is contributed by chitranayal` |

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## C#

`// C# program to implement the` `// above approach` `using` `System;` `class` `GFG{` ` ` `// Function to find the minimum` `// number of operations required` `// to obtain the string s` `static` `int` `minOperations(String s)` `{` ` ` `int` `n = s.Length;` ` ` `int` `pos = -1;` ` ` ` ` `// Iterate the string s` ` ` `for` `(` `int` `i = 0; i < s.Length; i++) ` ` ` `{` ` ` ` ` `// If first occurrence of 1` ` ` `// is found` ` ` `if` `(s[i] == ` `'1'` `)` ` ` `{` ` ` ` ` `// Mark the index` ` ` `pos = i;` ` ` `break` `;` ` ` `}` ` ` `}` ` ` ` ` `// Base case: If no 1 occurred` ` ` `if` `(pos == -1)` ` ` `{` ` ` ` ` `// No operations required` ` ` `return` `0;` ` ` `}` ` ` ` ` `// Stores the character` ` ` `// for which last operation` ` ` `// was performed` ` ` `int` `last = 1;` ` ` ` ` `// Stores minimum number` ` ` `// of operations` ` ` `int` `ans = 1;` ` ` ` ` `// Iterate from pos to n` ` ` `for` `(` `int` `i = pos + 1; i < n; i++)` ` ` `{` ` ` ` ` `// Check if s[i] is 0` ` ` `if` `(s[i] == ` `'0'` `)` ` ` `{` ` ` ` ` `// Check if last operation was` ` ` `// performed because of 1` ` ` `if` `(last == 1) ` ` ` `{` ` ` `ans++;` ` ` ` ` `// Set last to 0` ` ` `last = 0;` ` ` `}` ` ` `}` ` ` `else` ` ` `{` ` ` `if` `(last == 0) ` ` ` `{` ` ` ` ` `// Check if last operation was` ` ` `// performed because of 0` ` ` `ans++;` ` ` ` ` `// Set last to 1` ` ` `last = 1;` ` ` `}` ` ` `}` ` ` `}` ` ` ` ` `// Return the answer` ` ` `return` `ans;` `}` ` ` `// Driver code` `public` `static` `void` `Main(` `string` `[] args)` `{` ` ` `String s = ` `"10111"` `;` ` ` ` ` `Console.Write(minOperations(s));` `}` `}` ` ` `// This code is contributed by rock_cool` |

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**Output:**

3

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

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