www.youtube.com In this video, we provide a detailed explanation of Question 3 from Japan’s 2025 FE Examination Section B Public Sample Problems. This question focuses on the stack, a frequently tested data structure in algorithms and programming, and evaluates your understanding of the LIFO (Last-In, First-Out) principle along with the basic implementation using arrays. In this problem, a global integer array named stack with four elements and a global variable stackPos, which indicates the next position where a value will be stored, are used to implement the stack. One characteristic of this implementation is that the first element of the array is treated as position 1. Based on this specification, we analyze the correct behavior of the push and pop operations and identify the expressions that should be placed in blanks a and b. For the push operation, since stackPos always indicates the next available position, the correct action is to store the value at index stackPos of the array. After storing the value, stackPos must be incremented by one to update the position for the next insertion. For the pop operation, the stack must return the most recently inserted value according to the LIFO rule. Because stackPos indicates the next empty position, the value to be retrieved is located at stackPos minus one. Therefore, stackPos must be decremented by one before the value is accessed, ensuring that the correct element at the top of the stack is returned. Based on this reasoning, the correct combination of expressions for blanks a and b is choice “イ.” A clear understanding of how the stack operates and how array indices relate to stack behavior is essential for interpreting the program correctly. By firmly grasping these fundamental stack operations, you will significantly improve your ability to solve similar problems in Section B. Use this explanation to strengthen your understanding of basic data structures.
