[LeetCode]题解(python):150-Evaluate Reverse Polish Notation
题目来源:
https://leetcode.com/problems/evaluate-reverse-polish-notation/
题意分析:
给定一个数组,用这个数组来表示加减乘除,例如
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
题目思路:
这里考虑的是栈的使用。如果是数字那么push进栈,如果不是,那么把栈后两个数pop出来,进行相应的操作。要注意的是除法的时候要保证先转化正负一致再进行计算。
代码(python):
class Solution(object):
def evalRPN(self, tokens):
"""
:type tokens: List[str]
:rtype: int
"""
ans = []
for i in tokens:
if i != '/' and i != '*' and i != '+' and i != '-':
ans.append(int(i))
else:
tmp1 = ans.pop()
tmp2 = ans.pop()
if i == '/':
if tmp1*tmp2 < 0:
ans.append(-((-tmp2) // tmp1))
else:
ans.append(tmp2/tmp1)
if i == '*':
ans.append(tmp2*tmp1)
if i == '+':
ans.append(tmp2 + tmp1)
if i == '-':
ans.append(tmp2 - tmp1)
return ans[0]
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