LeetCode-Evaluate Reverse Polish Notation (Python)
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【问题】
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +
, -
, *
, /
.
Each operand may be an integer or another expression.
Some examples:
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9 ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
【代码】
class Solution: # @param tokens, a list of string # @return an integer def evalRPN(self, tokens): stack = [] for item in tokens: if item not in ("+", "-", "*", "/"): stack.append(int(item)) else: op2 = stack.pop() op1 = stack.pop() if item == "+": stack.append(op1 + op2) elif item == "-": stack.append(op1 - op2) elif item == "*": stack.append(op1 * op2) elif item == "/": stack.append(int(op1 *1.0 / op2)) return stack[0]
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