3191. Minimum Operations to Make Binary Array Elements Equal to One I

Problem Link

Description

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You are given a binary array nums.

You can do the following operation on the array any number of times (possibly zero):

• Choose any 3 consecutive elements from the array and flip all of them.

Flipping an element means changing its value from 0 to 1, and from 1 to 0.

Return the minimum number of operations required to make all elements in nums equal to 1. If it is impossible, return -1.

 

Example 1:

Input: nums = [0,1,1,1,0,0]

Output: 3

Explanation:
We can do the following operations:

• Choose the elements at indices 0, 1 and 2. The resulting array is nums = [1,0,0,1,0,0].
• Choose the elements at indices 1, 2 and 3. The resulting array is nums = [1,1,1,0,0,0].
• Choose the elements at indices 3, 4 and 5. The resulting array is nums = [1,1,1,1,1,1].

Example 2:

Input: nums = [0,1,1,1]

Output: -1

Explanation:
It is impossible to make all elements equal to 1.

 

Constraints:

• 3 <= nums.length <= 105
• 0 <= nums[i] <= 1

Solution

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Python3

class Solution:
    def minOperations(self, nums: List[int]) -> int:
        N = len(nums)
        first = second = third = res = 0
 
        for i, x in enumerate(nums):
            if (x + first) % 2 == 0:
                if i + 2 >= N: return -1
 
                first, second, third = second + 1, third + 1, 0
                res += 1
            else:
                first, second, third = second, third, 0
 
        return res