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leetcode/problem/number-of-equivalent-domino-pairs.html

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+<p>Given a list of <code>dominoes</code>, <code>dominoes[i] = [a, b]</code> is <strong>equivalent to</strong> <code>dominoes[j] = [c, d]</code> if and only if either (<code>a == c</code> and <code>b == d</code>), or (<code>a == d</code> and <code>b == c</code>) - that is, one domino can be rotated to be equal to another domino.</p>
+
+<p>Return <em>the number of pairs </em><code>(i, j)</code><em> for which </em><code>0 &lt;= i &lt; j &lt; dominoes.length</code><em>, and </em><code>dominoes[i]</code><em> is <strong>equivalent to</strong> </em><code>dominoes[j]</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> dominoes = [[1,2],[2,1],[3,4],[5,6]]
+<strong>Output:</strong> 1
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> dominoes = [[1,2],[1,2],[1,1],[1,2],[2,2]]
+<strong>Output:</strong> 3
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= dominoes.length &lt;= 4 * 10<sup>4</sup></code></li>
+	<li><code>dominoes[i].length == 2</code></li>
+	<li><code>1 &lt;= dominoes[i][j] &lt;= 9</code></li>
+</ul>