Leetcode Problem 2552. Count Increasing Quadruplets

2552. Count Increasing Quadruplets

Leetcode Solutions

Prefix and Suffix Sum Approach

  1. Initialize two 2D arrays ls and rs for storing prefix and suffix sums respectively.
  2. Fill the ls array with counts of elements less than nums[j] for each index j.
  3. Fill the rs array with counts of elements greater than nums[i] for each index i.
  4. Compute prefix sums for the ls array and suffix sums for the rs array.
  5. Iterate over all pairs of indices j and k such that j < k.
  6. If nums[j] > nums[k], calculate the product of the number of valid i indices (from ls[k]) and the number of valid l indices (from rs[j]).
  7. Add this product to the answer for each valid pair of j and k.
  8. Return the final answer.
UML Thumbnail

Naive Brute Force Approach

Ask Question

Programming Language
image/screenshot of info(optional)
Full Screen
Loading...

Suggested Answer

Answer
Full Screen
Copy Answer Code
Loading...