[LeetCode] 150. Evaluate Reverse Polish Notation

Problem : https://leetcode.com/problems/evaluate-reverse-polish-notation/

Use stack to cache operand and operator.

In python,  6 / -132 = -1.  To get the same result as C division operator, use int( 6 / -132 ) instead.

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        stack = []
        
        operators = { '+' : lambda a, b: a + b,    \
                      '-' : lambda a, b: a - b,    \
                      '*' : lambda a, b: a * b,    \
                      '/' : lambda a, b: int(a/b) }
        
        for t in tokens:
            opt = operators.get(t)
            if opt:
                b = stack.pop()
                a = stack.pop()
                
                c = opt(a, b)
                stack.append(c)
            else:
                stack.append(int(t))
    
        return stack.pop()

Edited on 05/25/2021. Simplify condition checks.