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StackUsingTwoQueues.py
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StackUsingTwoQueues.py
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# Problem Description: https://practice.geeksforgeeks.org/problems/stack-using-two-queues/1
import atexit
import io
import sys
# Contributed by : Nagendra Jha
_INPUT_LINES = sys.stdin.read().splitlines()
input = iter(_INPUT_LINES).__next__
_OUTPUT_BUFFER = io.StringIO()
sys.stdout = _OUTPUT_BUFFER
@atexit.register
def write():
sys.__stdout__.write(_OUTPUT_BUFFER.getvalue())
queue_1 = [] # first queue
queue_2 = [] # second queue
if __name__ == '__main__':
test_cases = int(input())
for cases in range(test_cases):
n = int(input())
a = list(map(int, input().strip().split()))
i = 0
while i < len(a):
if a[i] == 1:
push_in_stack(a[i+1])
i += 1
else:
print(pop_from_stack(), end=" ")
i += 1
# clear both the queues
queue_1 = []
queue_2 = []
print()
def push_in_stack(x):
# global declaration
global queue_1
global queue_2
if(len(queue_2) == 0):
queue_1.append(x)
else:
queue_2.append(x)
def pop_from_stack():
'''
:return: the value of top of stack and pop from it.
'''
# global declaration
global queue_1
global queue_2
val = -1
if(len(queue_1) == 0 and len(queue_2) == 0):
return val
elif(len(queue_1) == 0):
while(len(queue_2) > 1):
queue_1.append(queue_2[0])
del queue_2[0]
val = queue_2[0]
del queue_2[0]
else:
while(len(queue_1) > 1):
queue_2.append(queue_1[0])
del queue_1[0]
val = queue_1[0]
del queue_1[0]
return val