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Author: koralkulacoglu

LeetCode/4217-first-element-with-unique-frequency/README.md

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+<p>You are given an integer array <code>nums</code>.</p>
+
+<p>Return an integer denoting the <strong>first</strong> element (scanning from left to right) in <code>nums</code> whose <strong>frequency</strong> is <strong>unique</strong>. That is, no other integer appears the same number of times in <code>nums</code>. If there is no such element, return -1.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">nums = [20,10,30,30]</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">30</span></p>
+
+<p><strong>Explanation:</strong></p>
+
+<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>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">nums = [20,20,10,30,30,30]</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">20</span></p>
+
+<p><strong>Explanation:</strong></p>
+
+<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>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">nums = [10,10,20,20]</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">-1</span></p>
+
+<p><strong>Explanation:</strong></p>
+
+<ul>
+	<li>10 appears twice.</li>
+	<li>20 appears twice.</li>
+	<li>No element has a unique frequency.</li>
+</ul>
+</div>
+
+<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>5</sup></code></li>
+</ul>

LeetCode/4217-first-element-with-unique-frequency/solution.cpp

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+class Solution {
+public:
+    int firstUniqueFreq(vector<int>& nums) {
+        unordered_map<int, int> freq;
+        for (int i : nums) freq[i]++;
+        unordered_map<int, int> freqB;
+        for (auto i : freq) freqB[i.second]++;
+        for (int i : nums) {
+            if (freqB[freq[i]] == 1) return i;
+        }
+        return -1;
+    }
+};