Is Minimum Flips to Make Binary String Coherent easy or hard?

The problem is typically classified as Medium because the brute-force idea is straightforward but the optimal O(n) greedy transition is less obvious. Candidates must recognize that only boundary violations matter and update the minimum flips dynamically during traversal.

Minimum Flips to Make Binary String Coherent Python/Java solution

Implement a linear scan that tracks ones_seen and flips. For each character, increment ones_seen when you see '1'. When you encounter '0', update flips = min(flips + 1, ones_seen). The same logic translates directly to Python, Java, or C++ because it uses only primitive variables and a single loop.

How to solve Minimum Flips to Make Binary String Coherent in O(n)?

Perform a single left-to-right scan. Track the number of 1s seen and the minimum flips needed so far. When encountering a 0 after 1s, update flips using min(previous_flips + 1, ones_seen). This dynamic decision ensures the string remains monotonic while minimizing flips.

What is the best approach for Minimum Flips to Make Binary String Coherent?

The greedy single-pass approach is the most efficient. It scans the string once while maintaining the number of 1s seen and the minimum flips required so far. Each time a conflicting character appears, the algorithm decides whether flipping the current bit or previous bits is cheaper. This achieves O(n) time and O(1) space.

Is Minimum Flips to Make Binary String Coherent asked at Google/Amazon/Meta?

Binary string transformation problems with flip minimization frequently appear in interviews at large tech companies such as Google, Amazon, and Meta. Variants include making strings monotonic, minimizing bit changes, or enforcing ordering constraints using greedy or dynamic programming techniques.

What data structure is used in Minimum Flips to Make Binary String Coherent?

The optimal solution does not require complex data structures. It relies on simple counters and sequential array/string traversal. Some implementations use prefix arrays for counting zeros and ones, while the most optimized version maintains constant-space counters.

What is the time complexity of Minimum Flips to Make Binary String Coherent?

The optimal solution runs in O(n) time because it processes each character exactly once. Only a few counters are updated during the scan, so the space complexity remains O(1). Brute force approaches that test every split can take O(n^2) time.

3922. Minimum Flips to Make Binary String Coherent - Practice Online

You are given a binary string s.

A string is considered coherent if it does not contain "011" or "110" as subsequences.

In one operation, you can flip any character in s ('0' to '1' or '1' to '0').

Return an integer denoting the minimum number of modifications required to make s coherent.

A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.

Example 1:

Input: s = "1010"

Output: 1

Explanation:

Flip s[0] to get "0010", which contains no "011" or "110" subsequences.

Example 2:

Input: s = "0110"

Output: 1

Explanation:

Flip s[1] to get "0010", removing all forbidden subsequences "011" and "110".

Example 3:

Input: s = "1000"

Output: 0

Explanation:

The string already has no "011" or "110" subsequences, so no flips are needed.

Constraints:

1 <= s.length <= 10⁵
s[i] is either '0' or '1'.