Given a set of coin denominations and a target amount, find the minimum number of coins needed to reach that amount. You can assume you have an unlimited supply of each coin type.

Find the most frequent word in a given paragraph, excluding a list of banned words. Return the most common word after performing case-insensitive comparison and removing punctuation.

Find the maximum depth (number of nodes along the longest path from the root) of an N-ary tree. Each node can have multiple children.