Simplified question descriptions:

Q1
Given array nums and int k, find the k-th largest subarray bitwise OR.

Key Idea: If we start at any index i and look at OR values of subarrays, the resulting sequence is non-decreasing, and hence at most will be 31 unique values (32 bit ints). So, Keep track of only unique OR values, use dict to store val:cnt, and return kth largest accordingly.

Q2
Return index of kth next greater element for all indices of a given integer array.
example: [3,4,2,6,5], k=2
3 -> [4,6,5] -> 6 -> 4 (index in og array, 1-indexed)
4 -> [6,5] -> 5 -> 5
and so on for all elements.

I couldn't solve this question completely :( , please explain the solution in comments.

Q3
N nodes, complete undirected graph, some edges have 1 weight, rest have 0 weight. Return weight of MST.

Key Idea: You need k-1 edges to connect k islands.