March-150. Inverse Polish expression evaluation

 

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        f1 = lambda x,y:x+y
        f2 = lambda x,y:x-y
        f3 = lambda x,y:x*y
        f4 = lambda x,y:int(x/y)

        dic = {'+':f1,'-':f2,'*':f3,'/':f4}
        stack = []
        for i in tokens:
            if i in dic:
                x, y = stack.pop(),stack.pop()
                stack.append(dic[i](y,x))
            else:
                stack.append(int(i))
        
        print(stack)
        return stack[-1]

• Topic analysis
  • Given a character number group, which contains addition, subtraction, multiplication and division 
  • Define 4 functions with lambda in advance, and map them to the hash table according to the operation symbols
  • If it is a number directly into the stack, if it is not a number, then pop out the stack for calculation, and then push the result of the calculation into the stack