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  1. Queue using Two Stacks
  2. Discussions

Queue using Two Stacks

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56 Discussions

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  • ldiamond
     + 0 comments

    There's a typo in the sample input.

    1 14 enqueue 42

    This line should read

    1 14 enqueue 14

  • hank_ring
     + 0 comments
    q = []
for s in [input() for _ in range(int(input()))]:
    q.append(s[2:]) if s[0] == '1' else q.pop(0) if s == '2' else print(q[0]) if s == '3' else ...

  • yashdeora98294
     + 0 comments

    here is hackerrank queue using two stacks problem solution in Python, Java, C++, C and javascript

  • jcechace
     + 0 comments

    Skipped this one as I didn't want to write all the reading code. Regardles the idea for the implementation

    • enqueue = push to inStack
    • dequeue = iff outStack is empty pop everything from inStack while pushing to outStack; pop from outStack

    time complexity: enqueue is constant O(1) dequeue is also constant O(2) -- while taking any single element from the queue is linear in worst case (when outStack is empty), amortised complexity (taking N elementes) will result in 2 operations per element (one to move the element from inStack to outStack and one to take it from the outStack).

    de

  • gtai_quant
     + 0 comments
    class Stack:
    def __init__(self):
        self.items = []
        
    def push(self, x):
        self.items.append(x)
    
    def pop(self):
        if self.items:
            return self.items.pop()
        else:
            return None
            
    def top(self):
        if self.items:
            return self.items[-1]
        else:
            return None
            
class Queue:
    def __init__(self):
        self.en_st = Stack()  # enqueue stack
        self.de_st = Stack()  # dequeue stack
        
    def enqueue(self, x):
        self.en_st.push(x)
        
    def dequeue(self):
        if not self.de_st.items:
            while self.en_st.items:
                self.de_st.push(self.en_st.pop())
        return self.de_st.pop()
    
    def front(self):
        if not self.de_st.items:
            while self.en_st.items:
                self.de_st.push(self.en_st.pop())
        return self.de_st.top()

queue = Queue()
count = int(input())
for _ in range(count):
    order = input().split()
    if order[0] == '1':
        queue.enqueue(int(order[1]))
    elif order[0] == '2':
        queue.dequeue()
    elif order[0] == '3':
        print(queue.front())
    else:
        print('Error code: 999')
        break