2552. Count Increasing Quadruplets

LeetCodeArrayDynamic ProgrammingBinary Indexed TreeEnumerationPrefix SumOpen on judge ↗

Given a 0-indexed integer array nums of size n containing all numbers from 1 to n, return the number of increasing quadruplets. A quadruplet (i, j, k, l) is increasing if: - 0 <= i < j < k < l < n, and - nums[i] < nums[k] < nums[j] < nums[l]. Example 1: Input: nums = [1,3,2,4,5] Output: 2 Explanation: - When i = 0, j = 1, k = 2, and l = 3, nums[i] < nums[k] < nums[j] < nums[l]. - When i = 0

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