150. Evaluate Reverse Polish Notation

150. Evaluate Reverse Polish Notation

 

https://youtu.be/iu0082c4HDE?si=iSLrPASvJdT_CGH-

 

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:        
        stack = []

        for c in tokens:
            if c == "+":
                a, b = stack.pop(), stack.pop()
                stack.append(a + b)
            elif c == "-":
                a, b = stack.pop(), stack.pop()
                stack.append(b - a) # 빼는 순서 중요!!
            elif c == "*":
                a, b = stack.pop(), stack.pop()
                stack.append(a * b)
            elif c == "/":
                a, b = stack.pop(), stack.pop()
                stack.append(int(b / a)) # 나누는 순서 중요!!
            else:
                stack.append(int(c))
            
        #print(stack)
        return stack[0]