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leetcode/problem/number-of-good-pairs.html

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+<p>Given an array of integers <code>nums</code>, return <em>the number of <strong>good pairs</strong></em>.</p>
+
+<p>A pair <code>(i, j)</code> is called <em>good</em> if <code>nums[i] == nums[j]</code> and <code>i</code> &lt; <code>j</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [1,2,3,1,1,3]
+<strong>Output:</strong> 4
+<strong>Explanation:</strong> There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [1,1,1,1]
+<strong>Output:</strong> 6
+<strong>Explanation:</strong> Each pair in the array are <em>good</em>.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [1,2,3]
+<strong>Output:</strong> 0
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= nums.length &lt;= 100</code></li>
+	<li><code>1 &lt;= nums[i] &lt;= 100</code></li>
+</ul>