I thought of data structures when I thought of coding tests, so it often felt difficult. I was glad to have the opportunity to learn it properly this time. Thank you for the detailed data structure operation principle image. As I listened, I saw that in practical code, Steam is used to process entrySet().stream() or values().stream(), and I often used the code of my team members without knowing it, but I was glad to be able to learn it clearly this time. Thank you for the good data :)