You're given counts of 'A', 'B', and 'AB' strings. Combine them to construct the longest possible string where no two adjacent characters are the same.

You're given a grid where some cells have stones and others are empty. Find the minimum number of moves to redistribute the stones so that each cell has exactly one stone.

You're given a binary tree. Determine the minimum number of swaps needed at each level to sort the node values in ascending order.