1664. Ways to Make a Fair Array

https://leetcode.com/problems/ways-to-make-a-fair-array

Description

You are given an integer array nums. You can choose exactly one index (0-indexed) and remove the element. Notice that the index of the elements may change after the removal.

For example, if nums = [6,1,7,4,1]:

• Choosing to remove index 1 results in nums = [6,7,4,1].

• Choosing to remove index 2 results in nums = [6,1,4,1].

• Choosing to remove index 4 results in nums = [6,1,7,4].

An array is fair if the sum of the odd-indexed values equals the sum of the even-indexed values.

Return the number of indices that you could choose such that after the removal, numsis fair.

Example 1:

**Input:** nums = [2,1,6,4]
**Output:** 1
**Explanation:**
Remove index 0: [1,6,4] -> Even sum: 1 + 4 = 5. Odd sum: 6. Not fair.
Remove index 1: [2,6,4] -> Even sum: 2 + 4 = 6. Odd sum: 6. Fair.
Remove index 2: [2,1,4] -> Even sum: 2 + 4 = 6. Odd sum: 1. Not fair.
Remove index 3: [2,1,6] -> Even sum: 2 + 6 = 8. Odd sum: 1. Not fair.
There is 1 index that you can remove to make nums fair.

Example 2:

**Input:** nums = [1,1,1]
**Output:** 3
**Explanation:** You can remove any index and the remaining array is fair.

Example 3:

**Input:** nums = [1,2,3]
**Output:** 0
**Explanation:** You cannot make a fair array after removing any index.

Constraints:

• 1 <= nums.length <= 105

• 1 <= nums[i] <= 104

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