leetcode-problemset/leetcode-cn/problem (English)/统计好三元组(English) [count-good-triplets].html

<p>Given an array of integers <code>arr</code>, and three integers&nbsp;<code>a</code>,&nbsp;<code>b</code>&nbsp;and&nbsp;<code>c</code>. You need to find the number of good triplets.</p>

<p>A triplet <code>(arr[i], arr[j], arr[k])</code>&nbsp;is <strong>good</strong> if the following conditions are true:</p>

<ul>
	<li><code>0 &lt;= i &lt; j &lt; k &lt;&nbsp;arr.length</code></li>
	<li><code>|arr[i] - arr[j]| &lt;= a</code></li>
	<li><code>|arr[j] - arr[k]| &lt;= b</code></li>
	<li><code>|arr[i] - arr[k]| &lt;= c</code></li>
</ul>

<p>Where <code>|x|</code> denotes the absolute value of <code>x</code>.</p>

<p>Return<em> the number of good triplets</em>.</p>

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

<pre>
<strong>Input:</strong> arr = [3,0,1,1,9,7], a = 7, b = 2, c = 3
<strong>Output:</strong> 4
<strong>Explanation:</strong>&nbsp;There are 4 good triplets: [(3,0,1), (3,0,1), (3,1,1), (0,1,1)].
</pre>

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

<pre>
<strong>Input:</strong> arr = [1,1,2,2,3], a = 0, b = 0, c = 1
<strong>Output:</strong> 0
<strong>Explanation: </strong>No triplet satisfies all conditions.
</pre>

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

<ul>
	<li><code>3 &lt;= arr.length &lt;= 100</code></li>
	<li><code>0 &lt;= arr[i] &lt;= 1000</code></li>
	<li><code>0 &lt;= a, b, c &lt;= 1000</code></li>
</ul>