Implement Queue using Stacks
Implement a FIFO queue using only two stacks. Support push, pop (remove front), peek (get front), and empty.
Output the result of pop, peek, and empty operations.
Example:
push,1;push,2;peek;pop;empty
1 1 False
- We start with an empty queue and apply the given operations in sequence:
push,1andpush,2add elements 1 and 2 to the queue. - The
peekoperation returns the front element of the queue, which is 1, since the queue is implemented as a FIFO data structure. - The
popoperation removes the front element from the queue, which is also 1, and returns it. - The
emptyoperation checks if the queue is empty after thepopoperation; since there is still one element (2) left in the queue, it returnsFalse.
Constraints:
- 1 <= val <= 9
- At most 100 operations
- All pop and peek calls are valid
Background Knowledge
The problem requires implementing a FIFO (First-In-First-Out) queue using only two stacks. A queue is a data structure that follows the FIFO principle, meaning the first element added to the queue will be the first one to be removed. On the other hand, a stack is a LIFO (Last-In-First-Out) data structure, where the last element added to the stack will be the first one to be removed. To implement a queue using stacks, we need to understand how to utilize the LIFO nature of stacks to achieve the FIFO behavior of a queue.
The key concept here is to use two stacks to decouple the enqueuing (adding elements to the queue) and dequeuing (removing elements from the queue) operations. We can use one stack for enqueuing and the other stack for dequeuing. By doing so, we can ensure that the elements are added and removed in the correct order, following the FIFO principle. Understanding the push and pop operations on a stack is crucial, as these operations will be used to implement the queue operations.
To support the push, pop, peek, and empty operations, we need to consider how to handle the elements in the stacks. The push operation will add an element to the end of the queue, the pop operation will remove the element from the front of the queue, the peek operation will return the element at the front of the queue without removing it, and the empty operation will check if the queue is empty. We need to think about how to use the two stacks to implement these operations efficiently.
Algorithm/Approach
The general approach to solve this problem is to use two stacks to implement the queue. One stack will be used to store the new elements added to the queue (enqueuing), and the other stack will be used to store the elements in the correct order for removal (dequeuing). We can use the LIFO nature of the stacks to our advantage by reversing the order of the elements when moving them from one stack to the other. This approach will allow us to achieve the FIFO behavior required by the queue.
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