Coin Change II Coding Problem Explained

Coin Change II is a classic dynamic programming problem that focuses on counting combinations, not finding the minimum coins. You are given an array of coin denominations and a target amount. Your task is to determine how many different ways you can make up that amount using the given coins. Each coin can be used an unlimited number of times. The order of coins does not matter. That detail is critical. For example, if the amount is 5 and the coins are [1, 2, 5], then 1 + 2 + 2 and 2 + 1 + 2 are considered the same combination, not different ones. This problem often appears in interviews because it tests whether you understand the difference between combinations and permutations, and whether you can design a dynamic programming solution that avoids double-counting. Why many first attempts go wrong A common mistake is to treat this like a permutation problem. If you build solutions by trying all coin choices at every step, you’ll end up counting the same combination multiple times in dif