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+--- Thread: Reverse Polish Notation (/showthread.php?tid=63648)
Reverse Polish Notation - Imagine - 2013-04-06
A tutorial that my teacher linked shows 9 7 - 2 / being invalid, but I don't see how it is.
My thought process:
After 9, 7 is read in, stack is:
7
9
- is read in, 9 and 7 is popped off, and 9 - 7 is pushed in:
2
The 2 after - is read in and pushed in:
2
2
/ is read in, leading to both 2's being popped off and 2/2 to be pushed in:
1
The tutorial shows that right after 9 -7 is calculated, two numbers are attempted to be popped off the stack, leading to an error because the stack currently only has 1 number in it. Am I doing something wrong?
Reverse Polish Notation - Locked - 2013-04-06
It can also be 2 9 7 - / for it to work.
If you want to visualize it:
| Input | Operation | Stack |
|---|---|---|
| 2 | Push Back | [2] |
| 9 | Push Back | [2,9] |
| 7 | Push Back | [2,9,7] |
| - | Subtract | [2,(9-7)] |
| - | Push Result | [2,2] |
| / | Divide | [(2/2)] |
| / | Push Result | [1] |
Likewise, I think yours is still correct.
| Input | Operation | Stack |
|---|---|---|
| 9 | Push Back | [9] |
| 7 | Push Back | [9,7] |
| - | Subtract | [9-7] |
| - | Push Result | [2] |
| 2 | Push Back | [2,2] |
| / | Divide | [2/2] |
| / | Push Result | [1] |