Same Python code returning different answer in Leetcode

July 25, 2023

when I do Leetcode questions I write the code in PyCharm on my PC and when it’s working I copy paste it into Leetcode.

This is the code I have written.

def main():
    # tokens = ["2", "1", "+", "3", "*"]
    # tokens = ["4", "13", "5", "/", "+"]
    tokens = ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]
    print(eval_rpn(tokens))


def eval_rpn(tokens):
    stack = []
    ops = ["+", "-", "*", "/"]

    for c in tokens:
        if c not in ops:
            stack.append(c)
        else:
            num2 = int(stack.pop())
            num1 = int(stack.pop())

            if c == "+":
                total = num1 + num2
            elif c == "-":
                total = num1 - num2
            elif c == "*":
                total = num1 * num2
            else:  # The only operator left is division
                total = num1 / num2

            stack.append(total)

    return stack[-1]


if __name__ == "__main__":
    main()

This is the code I have pasted and submitted in Leetcode.

class Solution(object):
    def evalRPN(self, tokens):
        stack = []
        ops = ["+", "-", "*", "/"]

        for c in tokens:
            if c not in ops:
                stack.append(c)
            else:
                num2 = int(stack.pop())
                num1 = int(stack.pop())

                if c == "+":
                    total = num1 + num2
                elif c == "-":
                    total = num1 - num2
                elif c == "*":
                    total = num1 * num2
                else:
                    total = num1 / num2

                stack.append(total)

        return stack[-1]

But for some reason for the input tokens = ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"] Leetcode returns 12. When I run the same code on my PC it returns 22. 22 is the expected output. Not 12.

Can anyone point out what I am doing wrong?

The Leetcode question

>Solution :

This is happening because of different version(Python 2.7) you might have selected in leetcode editor

And this is happening because of the way how python 2.7 handles negative number division , if you follow your code you will see at one point the value in stack would be -132 and then the subsequent division with 6 is making the result as -1