自分用メモ。データ構造とちょっとしたコードの例。 StackA stack is a last in, first out data structure. There are two main fundamental operation for stack: push and pop. The push operation adds an item to the top of the stack. The pop operation removes an item from the top of stack, and returns the value. We can implement the stack with linked list or array. Stacks are often used in the computing world. For example, expres