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
Hint 1Approach
Hint 2Approach
Hint 3Pseudocode
Hint 4Full solution