partition

K-th largest has three textbook solutions, and the signal is knowing Quickselect's average O(n) beats sorting's O(n log n), why its worst case is O(n²), and when a heap is actually the better call. Here is the answer.

This famously-hard problem wants better than the O(m+n) merge: an O(log) binary search on the partition. The signal is binary-searching the split point so the left halves stay below the right halves. Here is the answer.