mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
synced 2025-01-10 18:48:13 +08:00
49 lines
1.6 KiB
HTML
49 lines
1.6 KiB
HTML
<p>Given an integer array <code>nums</code>, return <em>the number of all the <strong>arithmetic subsequences</strong> of</em> <code>nums</code>.</p>
|
|
|
|
<p>A sequence of numbers is called arithmetic if it consists of <strong>at least three elements</strong> and if the difference between any two consecutive elements is the same.</p>
|
|
|
|
<ul>
|
|
<li>For example, <code>[1, 3, 5, 7, 9]</code>, <code>[7, 7, 7, 7]</code>, and <code>[3, -1, -5, -9]</code> are arithmetic sequences.</li>
|
|
<li>For example, <code>[1, 1, 2, 5, 7]</code> is not an arithmetic sequence.</li>
|
|
</ul>
|
|
|
|
<p>A <strong>subsequence</strong> of an array is a sequence that can be formed by removing some elements (possibly none) of the array.</p>
|
|
|
|
<ul>
|
|
<li>For example, <code>[2,5,10]</code> is a subsequence of <code>[1,2,1,<strong><u>2</u></strong>,4,1,<u><strong>5</strong></u>,<u><strong>10</strong></u>]</code>.</li>
|
|
</ul>
|
|
|
|
<p>The test cases are generated so that the answer fits in <strong>32-bit</strong> integer.</p>
|
|
|
|
<p> </p>
|
|
<p><strong class="example">Example 1:</strong></p>
|
|
|
|
<pre>
|
|
<strong>Input:</strong> nums = [2,4,6,8,10]
|
|
<strong>Output:</strong> 7
|
|
<strong>Explanation:</strong> All arithmetic subsequence slices are:
|
|
[2,4,6]
|
|
[4,6,8]
|
|
[6,8,10]
|
|
[2,4,6,8]
|
|
[4,6,8,10]
|
|
[2,4,6,8,10]
|
|
[2,6,10]
|
|
</pre>
|
|
|
|
<p><strong class="example">Example 2:</strong></p>
|
|
|
|
<pre>
|
|
<strong>Input:</strong> nums = [7,7,7,7,7]
|
|
<strong>Output:</strong> 16
|
|
<strong>Explanation:</strong> Any subsequence of this array is arithmetic.
|
|
</pre>
|
|
|
|
<p> </p>
|
|
<p><strong>Constraints:</strong></p>
|
|
|
|
<ul>
|
|
<li><code>1 <= nums.length <= 1000</code></li>
|
|
<li><code>-2<sup>31</sup> <= nums[i] <= 2<sup>31</sup> - 1</code></li>
|
|
</ul>
|