Consider a stack π and a queue π. Both of them are initially empty and haveβ¦
2026
Consider a stack π and a queue π. Both of them are initially empty and have the capacity to store ten elements each. The elements 1, 2, 3, 4, and 5 arrive one by one, in that order. When an element arrives, it is assigned either to π (pushed on π ) or to π (enqueued to π). Once all the five elements are stored, the output is generated in two steps. First, stack S is emptied by popping all elements. Then queue π is emptied by dequeueing all elements. The output obtained by following this process is 4 3 1 2 5 .
Given the output, the objective is to predict whether an element was assigned to π or π.
Which of the following options is/are possible valid assignment(s) of the elements?
Note: In the options, the notation π₯π denotes that element π₯ was assigned to π and π¦π denotes that element π¦ was assigned to π.
- A.
1π, 2π, 3π, 4π, 5Q
- B.
1π, 2π, 3π, 4π, 5Q
- C.
1π, 2π, 3π, 4π, 5S
- D.
1π, 2π, 3π, 4π, 5π
Attempted by 28 students.
Show answer & explanation
Correct answer: A, B
Step 1: Analyze Output Structure The output 4 3 1 2 5 is generated in two phases. First, Stack S is emptied (popped). Second, Queue Q is emptied (dequeued). Thus, 4 3 1 comes from S, and 2 5 comes from Q.
Step 2: Analyze Stack S Stack is LIFO (Last In First Out). Output 4 3 1 means 4 was pushed last, then 3, then 1. So 1, 3, 4 must be in S.
Step 3: Analyze Queue Q Queue is FIFO (First In First Out). Output 2 5 means 2 was enqueued first, then 5. So 2, 5 must be in Q.
Step 4: Conclusion Valid assignment: 1S, 2Q, 3S, 4S, 5Q.