number-of-equivalent-domino-pairs

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Algorithms

Given a list of <code>dominoes</code>, <code>dominoes[i] = [a, b]</code> is equivalent to <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.

Return the number of pairs <code>(i, j)</code> for which <code>0 &lt;= i &lt; j &lt; dominoes.length</code>, and <code>dominoes[i]</code> is equivalent to <code>dominoes[j]</code>.

&nbsp;
Example 1:

<pre>
Input: dominoes = [[1,2],[2,1],[3,4],[5,6]]
Output: 1
</pre>

Example 2:

<pre>
Input: dominoes = [[1,2],[1,2],[1,1],[1,2],[2,2]]
Output: 3
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= dominoes.length &lt;= 4 * 104</code></li>
	<li><code>dominoes[i].length == 2</code></li>
	<li><code>1 &lt;= dominoes[i][j] &lt;= 9</code></li>
</ul>

numEquivDominoPairs

Number of Equivalent Domino Pairs

Array

Hash Table

Counting

给你一组多米诺骨牌 <code>dominoes</code> 。

形式上，<code>dominoes[i] = [a, b]</code> 与 <code>dominoes[j] = [c, d]</code> 等价 当且仅当 (<code>a == c</code> 且 <code>b == d</code>) 或者 (<code>a == d</code> 且 <code>b == c</code>) 。即一张骨牌可以通过旋转 <code>0</code>&nbsp;度或 <code>180</code> 度得到另一张多米诺骨牌。

在&nbsp;<code>0 &lt;= i &lt; j &lt; dominoes.length</code>&nbsp;的前提下，找出满足&nbsp;<code>dominoes[i]</code> 和&nbsp;<code>dominoes[j]</code>&nbsp;等价的骨牌对 <code>(i, j)</code> 的数量。

&nbsp;

示例 1：

<pre>
输入：dominoes = [[1,2],[2,1],[3,4],[5,6]]
输出：1
</pre>

示例 2：

<pre>
输入：dominoes = [[1,2],[1,2],[1,1],[1,2],[2,2]]
输出：3
</pre>

&nbsp;

提示：

<ul>
	<li><code>1 &lt;= dominoes.length &lt;= 4 * 104</code></li>
	<li><code>dominoes[i].length == 2</code></li>
	<li><code>1 &lt;= dominoes[i][j] &lt;= 9</code></li>
</ul>