Is Minimum Number of K Consecutive Bit Flips easy or hard?

LeetCode classifies this problem as Hard because the greedy insight is not immediately obvious. The challenge lies in efficiently tracking overlapping flip operations and avoiding repeated O(k) updates for every flip.

Minimum Number of K Consecutive Bit Flips Python/Java solution

Both Python and Java implementations typically follow the greedy sliding window pattern. Python solutions often use collections.deque for tracking flips, while Java implementations use ArrayDeque or simulate the window with integer markers. Both achieve O(n) time complexity.

How to solve Minimum Number of K Consecutive Bit Flips in O(n)?

Traverse the array while tracking how many flips are currently affecting the position. If the effective bit is 0, start a new flip window of length k. Maintain active flip parity using either a queue of start indices or an in-place marker technique so expired flips are removed as the window moves.

What is the best approach for Minimum Number of K Consecutive Bit Flips?

The best approach is a greedy sliding window algorithm that processes the array left to right. When the current effective bit becomes 0, a flip must start at that position. Tracking active flips using a queue or in-place markers ensures each element is processed once, resulting in O(n) time complexity.

Is Minimum Number of K Consecutive Bit Flips asked at Google/Amazon/Meta?

Variations of this problem appear in interviews at large tech companies including Google, Amazon, and Meta because it tests greedy reasoning, sliding window control, and efficient state tracking. Candidates must recognize that flips should be applied immediately when a 0 is encountered.

What data structure is used in Minimum Number of K Consecutive Bit Flips?

Common implementations use a queue or deque to track the starting indices of active flips. Some optimized solutions avoid extra structures by storing flip markers directly in the array and maintaining a running parity variable to simulate the sliding window.

What is the time complexity of Minimum Number of K Consecutive Bit Flips?

The optimal solutions run in O(n) time because each index is visited once while maintaining the effect of previous flips. Queue operations or window updates are constant time. Space complexity is O(k) for the queue version and O(1) for the in-place sliding window optimization.

Description Solution Video 1:03:24

995. Minimum Number of K Consecutive Bit Flips

Hard62.7% acceptance2 companies

You are given a binary array nums and an integer k.

A k-bit flip is choosing a subarray of length k from nums and simultaneously changing every 0 in the subarray to 1, and every 1 in the subarray to 0.

Return the minimum number of k-bit flips required so that there is no 0 in the array. If it is not possible, return -1.

A subarray is a contiguous part of an array.

Example 1:

Input: nums = [0,1,0], k = 1
Output: 2
Explanation: Flip nums[0], then flip nums[2].

Example 2:

Input: nums = [1,1,0], k = 2
Output: -1
Explanation: No matter how we flip subarrays of size 2, we cannot make the array become [1,1,1].

Example 3:

Input: nums = [0,0,0,1,0,1,1,0], k = 3
Output: 3
Explanation: 
Flip nums[0],nums[1],nums[2]: nums becomes [1,1,1,1,0,1,1,0]
Flip nums[4],nums[5],nums[6]: nums becomes [1,1,1,1,1,0,0,0]
Flip nums[5],nums[6],nums[7]: nums becomes [1,1,1,1,1,1,1,1]

Constraints: