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

Description

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

 

Solutions

Solution: Greedy

• Time complexity: O(n)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {number[]} nums
 * @return {number}
 */
const minOperations = function (nums) {
  const n = nums.length;
  let result = 0;

  for (let index = 0; index < n - 2; index++) {
    if (nums[index]) continue;

    nums[index + 1] ^= 1;
    nums[index + 2] ^= 1;
    result += 1;
  }

  return !nums[n - 2] || !nums[n - 1] ? -1 : result;
};