PRJAN15F  Stack Overflow
Stack is a basic data structure. Where 3 operation can be done

Push: You can push object to the stack

Pop: You can pop the object to the stack

Top: You can check the value of the top object.
For further details you can get idea here ( if you really don’t know ) : https://en.wikibooks.org/wiki/Data_Structures/Stacks_and_Queues
Now we have a problem here, there are N stack in front of you. they are numbered from 1 to N. Each of them are initially empty. Now you will have Q operations. Each operation can be one the below 4 types:

push i x, Push a value of x to stack numbered i

pop i, Pop value from the stack numbered i, if stack is empty discard the operation

put i j, Put the j’th stack on top of the i’th stack. So there will be no element left on the j’th stack.

top i, Print the value of the top element of ith stack. If stack is empty print “Empty!”
Check the Sample IO for further understanding…
Input:
Input starts with an integer T (≤5), denoting the number of test cases.
The first line of a case is a blank line. The next line contains two integers N (1 ≤ N ≤ 10^{4}), Q(1 ≤ Q ≤ 5*10^{4}).
The next Q lines will contain a operation like above mentioned.
(1≤ I, j ≤ N), (1≤ x ≤ 10^{5})
Output
For each test case, print the case number in a single line. Then for each 4th type operation you should print the value or “Empty!” if the stack is empty.
Input 
Output 
1 3 18 push 1 1 push 2 2 push 3 3 push 3 4 top 1 top 2 top 3 put 1 3 pop 2 top 1 top 2 top 3 pop 1 top 1 pop 1 top 1 pop 1 top 1 
Case 1: 1 2 4 4 Empty! Empty! 3 1 Empty! 
Judge data is huge so use faster IO like scanf/printf
Problemsetter: Ahmad Faiyaz
hide comments
nimphy:
20180523 10:15:50
Notice the Details！ 

nadstratosfer:
20171109 03:23:44
When solving with Python, note that input contains blanklines other than the ones mentioned in statement. Also, optimize or TLE. Last edit: 20180105 06:25:57 

mahmud2690:
20170716 15:01:57
Skip if i = j in "put" operation. 

Vipul Srivastava:
20160625 10:40:42
Last edit: 20160625 10:51:50 

topke:
20160212 10:29:07
@numerix Thats wierd i got WA by not checking put operation validity. Guess that should be stated in problem statement or removed from test cases 

Rishav Goyal:
20150808 19:57:43
that "i=j" helped alot to avoid WA. thanks shiva 

n3gativ3:
20150531 16:03:09
just remember to print Case No. :P 

aky:
20150304 10:03:31
Getting sigsegv... Is there any tricky test case? 

(Tjandra Satria Gunawan)(æ›¾æ¯…æ˜†):
20150227 00:07:04
Yo Dawg, getting Stack Overflow on Stack Overflow problem, so I can debug my buggy Stack Overflow code for this Stack Overflow problem :p :p 

numerix:
20150213 22:56:01
@Takanori MAEHARA: Thanks.

Added by:  Shafaet 
Date:  20150131 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 JSMONKEY 
Resource:  Progkriya Contest January 2015 