# 150. Evaluate Reverse Polish Notation
"""
given an array of strings 'tokens' that represents an arithmetic expression
in a reverse polish notation. evaluate the expression. return an integer that
represents the value of the expression. note that the valid operators are + -
and /. each operand may be an integer or another expression. the division
between two integers always truncates toward zero. there will not any
division by zero. the input represents a valid arithmetic expression in
reverse polish notation. the answer and all intermediate calculations can be
represented in a 32 bit integer.
"""
class Solution(object):
def evalRPN(self, tokens):
"""
:type tokens: List[str]
:rtype: int
"""
stack = []
for t in tokens:
if t not in "+-*/":
stack.append(int(t))
else:
r, l = stack.pop(), stack.pop()
if t == "+":
stack.append(l + r)
elif t == "-":
stack.append(l - r)
elif t == "*":
stack.append(l * r)
else:
stack.append(int(float(l) / r))
return stack.pop()
if __name__ == "__main__":
obj = Solution()
print(obj.evalRPN(tokens=["2", "1", "+", "3", "*"]))
print(obj.evalRPN(tokens=["4", "13", "5", "/", "+"]))
print(
obj.evalRPN(
tokens=["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]
)
)
