185. Stack From Two Queues
Core1000 ms256 MBSolved by 0%
The mirror of the previous problem: build a working STACK using only queues. You may add at the back, remove from the front, and read the front.
A queue preserves order, so getting the LAST value added to come out first takes real work. There are two standard ways, make adding expensive, or make removing expensive, and either is accepted here.
Constraints - `1 ≤ q ≤ 100000` - `-1000000 ≤ x ≤ 1000000`
Input
The first line contains an integer q, the number of operations.
Each of the next q lines is one operation:
- 1 x, push x
- 2, pop the top value and print it
- 3, print the top value without removing it
Output
Print one line for each 2 and 3 operation, the value, or Empty if the stack holds nothing.
Input5
1 10
1 20
3
2
3
Output20
20
10
Noteconfirms the LAST value pushed comes out first
Input2
2
3
OutputEmpty
Empty
Notereads an empty stack
Hints
Four rungs, in order. The last two open once you have submitted an attempt. A wrong one counts.
Hint 1Where to start
Hint 2The approachOpen hint 1 first. This one carries on from it.
Hint 3PseudocodeOpen hint 2 first. This one carries on from it.
Hint 4Full solutionOpen hint 3 first. This one carries on from it.