first-element-with-unique-frequency

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Algorithms

You are given an integer array <code>nums</code>.

Return an integer denoting the first element (scanning from left to right) in <code>nums</code> whose frequency is unique. That is, no other integer appears the same number of times in <code>nums</code>. If there is no such element, return -1.

&nbsp;
Example 1:

<div class="example-block">
Input: nums = [20,10,30,30]

Output: 30

Explanation:

<ul>
	<li>20 appears once.</li>
	<li>10 appears once.</li>
	<li>30 appears twice.</li>
	<li>The frequency of 30 is unique because no other integer appears exactly twice.</li>
</ul>
</div>

Example 2:

<div class="example-block">
Input: nums = [20,20,10,30,30,30]

Output: 20

Explanation:

<ul>
	<li>20 appears twice.</li>
	<li>10 appears once.</li>
	<li>30 appears 3 times.</li>
	<li>The frequency of 20, 10, and 30 are unique. The first element that has unique frequency is 20.</li>
</ul>
</div>

Example 3:

<div class="example-block">
Input: nums = [10,10,20,20]

Output: -1

Explanation:

<ul>
	<li>10 appears twice.</li>
	<li>20 appears twice.</li>
	<li>No element has a unique frequency.</li>
</ul>
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= nums.length &lt;= 105</code></li>
	<li><code>1 &lt;= nums[i] &lt;= 105</code></li>
</ul>