You are given an array representing the heights of vertical lines. Find two lines that, together with the x-axis, form a container that holds the most water.

Find two numbers in a given array that add up to a specific target value, and return their indices. Essentially, you need to efficiently locate the pair that satisfies the sum requirement.

Find the number of increasing quadruplets (i, j, k, l) in an array, where i < j < k < l and nums[i] < nums[k] < nums[j] < nums[l]. Count how many such quadruplets exist within the input array.