Given an array and a window size k, find the median of each sliding window.
Example: nums = [1,3,-1,-3,5,3,6,7], k=3 → Output: [1,-1,-1,3,5,6]
Explanation: Naive approach: sort each window and pick median.
Time Complexity: O(n k log k)
Space Complexity: O(k)
for i in 0..n-k: window = nums[i..i+k-1] sort(window) median = window[k//2] add median to result return result