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38 lines
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38 lines
1.4 KiB
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<p>Given a <strong>0-indexed</strong> integer array <code>nums</code> of size <code>n</code> containing all numbers from <code>1</code> to <code>n</code>, return <em>the number of increasing quadruplets</em>.</p>
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<p>A quadruplet <code>(i, j, k, l)</code> is increasing if:</p>
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<ul>
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<li><code>0 <= i < j < k < l < n</code>, and</li>
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<li><code>nums[i] < nums[k] < nums[j] < nums[l]</code>.</li>
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</ul>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> nums = [1,3,2,4,5]
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<strong>Output:</strong> 2
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<strong>Explanation:</strong>
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- When i = 0, j = 1, k = 2, and l = 3, nums[i] < nums[k] < nums[j] < nums[l].
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- When i = 0, j = 1, k = 2, and l = 4, nums[i] < nums[k] < nums[j] < nums[l].
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There are no other quadruplets, so we return 2.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> nums = [1,2,3,4]
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<strong>Output:</strong> 0
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<strong>Explanation:</strong> There exists only one quadruplet with i = 0, j = 1, k = 2, l = 3, but since nums[j] < nums[k], we return 0.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>4 <= nums.length <= 4000</code></li>
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<li><code>1 <= nums[i] <= nums.length</code></li>
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<li>All the integers of <code>nums</code> are <strong>unique</strong>. <code>nums</code> is a permutation.</li>
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</ul>
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