leetcode-problemset/leetcode-cn/problem (English)/数组中不等三元组的数目(English) [number-of-unequal-triplets-in-array].html

<p>You are given a <strong>0-indexed</strong> array of positive integers <code>nums</code>. Find the number of triplets <code>(i, j, k)</code> that meet the following conditions:</p>

<ul>
	<li><code>0 &lt;= i &lt; j &lt; k &lt; nums.length</code></li>
	<li><code>nums[i]</code>, <code>nums[j]</code>, and <code>nums[k]</code> are <strong>pairwise distinct</strong>.
	<ul>
		<li>In other words, <code>nums[i] != nums[j]</code>, <code>nums[i] != nums[k]</code>, and <code>nums[j] != nums[k]</code>.</li>
	</ul>
	</li>
</ul>

<p>Return <em>the number of triplets that meet the conditions.</em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [4,4,2,4,3]
<strong>Output:</strong> 3
<strong>Explanation:</strong> The following triplets meet the conditions:
- (0, 2, 4) because 4 != 2 != 3
- (1, 2, 4) because 4 != 2 != 3
- (2, 3, 4) because 2 != 4 != 3
Since there are 3 triplets, we return 3.
Note that (2, 0, 4) is not a valid triplet because 2 &gt; 0.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,1,1,1,1]
<strong>Output:</strong> 0
<strong>Explanation:</strong> No triplets meet the conditions so we return 0.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>3 &lt;= nums.length &lt;= 100</code></li>
	<li><code>1 &lt;= nums[i] &lt;= 1000</code></li>
</ul>