Ways to Make a Fair Array
<p>You are given an integer array&nbsp;<code>nums</code>. You can choose <strong>exactly one</strong> index (<strong>0-indexed</strong>) and remove the element. Notice that the index of the elements may change after the removal.</p>

<p>For example, if <code>nums = [6,1,7,4,1]</code>:</p>

<ul>
	<li>Choosing to remove index <code>1</code> results in <code>nums = [6,7,4,1]</code>.</li>
	<li>Choosing to remove index <code>2</code> results in <code>nums = [6,1,4,1]</code>.</li>
	<li>Choosing to remove index <code>4</code> results in <code>nums = [6,1,7,4]</code>.</li>
</ul>

<p>An array is <strong>fair</strong> if the sum of the odd-indexed values equals the sum of the even-indexed values.</p>

<p>Return the <em><strong>number</strong> of indices that you could choose such that after the removal, </em><code>nums</code><em> </em><em>is <strong>fair</strong>. </em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

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

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,1,1]
<strong>Output:</strong> 3
<strong>Explanation:</strong>&nbsp;You can remove any index and the remaining array is fair.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3]
<strong>Output:</strong> 0
<strong>Explanation:</strong>&nbsp;You cannot make a fair array after removing any index.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>4</sup></code></li>
</ul>
Array; Prefix Sum
func waysToMakeFair(nums []int) (ans int) {
	var s1, s2, t1, t2 int
	for i, v := range nums {
		if i%2 == 0 {
			s1 += v
		} else {
			s2 += v
		}
	}
	for i, v := range nums {
		if i%2 == 0 && t2+s1-t1-v == t1+s2-t2 {
			ans++
		}
		if i%2 == 1 && t2+s1-t1 == t1+s2-t2-v {
			ans++
		}
		if i%2 == 0 {
			t1 += v
		} else {
			t2 += v
		}
	}
	return
}