You have learned advanced greedy:
Huffman coding: : Merge smallest frequencies first using min-heap.
Reorganize string: : Place most frequent characters first using max-heap.
Remove K digits: : Use stack to maintain increasing order from left. Good job on finishing this section. You now have a complete greedy toolkit. You also saw:
Remove K digits: : Pop larger digits when smaller ones arrive.
Create maximum number: : Split, extract, merge with lexicographic comparison.
Patching array: : Extend range by doubling with patches. These patterns appear in many coding interviews.