# Even Frequency

Given a list of integers `nums`

, return whether all numbers appear an even number of times.

This should be done in \(\mathcal{O}(1)\) space.

**Constraints**

`n ≤ 100,000`

where`n`

is the length of`nums`

https://binarysearch.com/problems/Even-Frequency

## Examples

### Example 1

**Input**

- nums =
`[2, 4, 4, 2, 3, 3]`

**Output**

- answer =
`True`

**Explanation**

Every number occurs twice.

### Example 2

**Input**

- nums =
`[1]`

**Output**

- answer =
`False`

**Explanation**

`1`

occurs an odd number of times.

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