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29 lines
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29 lines
1.1 KiB
HTML
<p>For an integer array <code>nums</code>, an <strong>inverse pair</strong> is a pair of integers <code>[i, j]</code> where <code>0 <= i < j < nums.length</code> and <code>nums[i] > nums[j]</code>.</p>
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<p>Given two integers n and k, return the number of different arrays consist of numbers from <code>1</code> to <code>n</code> such that there are exactly <code>k</code> <strong>inverse pairs</strong>. Since the answer can be huge, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>
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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> n = 3, k = 0
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<strong>Output:</strong> 1
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<strong>Explanation:</strong> Only the array [1,2,3] which consists of numbers from 1 to 3 has exactly 0 inverse pairs.
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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> n = 3, k = 1
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> The array [1,3,2] and [2,1,3] have exactly 1 inverse pair.
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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>1 <= n <= 1000</code></li>
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<li><code>0 <= k <= 1000</code></li>
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</ul>
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