{ "data": { "question": { "questionId": "629", "questionFrontendId": "629", "boundTopicId": null, "title": "K Inverse Pairs Array", "titleSlug": "k-inverse-pairs-array", "content": "

For an integer array nums, an inverse pair is a pair of integers [i, j] where 0 <= i < j < nums.length and nums[i] > nums[j].

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Given two integers n and k, return the number of different arrays consist of numbers from 1 to n such that there are exactly k inverse pairs. Since the answer can be huge, return it modulo 109 + 7.

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Example 1:

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\nInput: n = 3, k = 0\nOutput: 1\nExplanation: Only the array [1,2,3] which consists of numbers from 1 to 3 has exactly 0 inverse pairs.\n
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Example 2:

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\nInput: n = 3, k = 1\nOutput: 2\nExplanation: The array [1,3,2] and [2,1,3] have exactly 1 inverse pair.\n
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Constraints:

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Most standard library headers are already included automatically for your convenience.

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OpenJDK 17 . Java 8 features such as lambda expressions and stream API can be used.

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Most standard library headers are already included automatically for your convenience.

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