Evaluate Reverse Polish Notation (RPN) - Leetcode 150 - Stacks (Python)

[@GregHogg]

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[@masemark87]

Best channel I’ve discovered this year! Great content, thank you

[@badrlakhal5440]

Pay attention, in Python 2, the / operator performs integer division, and rounds towards negative infinity. So 6/-132 gives -1, and of course int(6/-132) also gives -1. In Python 3, the / operator performs float division, so 6/-132 is -0.045. Then the int function truncates decimals, so int(6/-132) is 0.

[@JoeTan-nq4fq]

Using eval() for shorter code stack = [] # stack contains strings for c in tokens: if c in '+-*/': b, a = stack.pop(), stack.pop() stack.append(str(int(eval(a + c + b)))) else: stack.append(c) return int(stack[0])

[@ThePersopolis]

Could you not use stk.append( int(a / b) ) for division instead of the if/else and use of ceil and floor?

[@chucksneedmoreland]

I didnt know int() would do all that for you

[@yugaank100]

you can, it works

[@Sanu-k5c]

Hello there, when putting the condition for the token being a number in the if and it being an operator in the else part, why was there a problem with the pop() statement, error said as "pop from an empty list", ? Has it got something to do with the interpreter ? Although it works fine in vs code

[@mohitsonwane7031]

I feel that this statement in the question is the most important. "The division between two integers always truncates toward zero."

[@AliShahid-cp6bz]

Great content and dedication.

[@saleheen12]

Ceil and floor giving error in leetcode although in my local compiler the output is correct. Try this instead: int(float(a)/b)

[@haribshahbaz1237]

or just simply int(a / b). a / b already gives us a float, therefore converting a to float explicitly is not required.

[@anirbandas12]

For js/ ts ceil doesn't work i think i had to use trunc ..

[@VitaliyBorisok]

Noticed that in Java implementation you also used ceil and floor. But it is redundant for integer division. It always drops the part after dot.

[@moonlight-td8ed]

or we can just append int(a/b)