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

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Hung

Leetcode

You are given a

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

Analysis

Since we can only flip three consecutive elements at a time, isolated 0s or certain patterns of 0s may prevent us from turning everything into 1. If the number of 0s in certain positions makes it impossible to fully eliminate them using groups of three, the transformation cannot be achieved.