leetcode-mid-others-150. Evaluate Reverse Polish Notation
mycode 42.30%、
注意:如果不考虑符号,-1//3=-1而不是等于0,因为是向下取整
class Solution(object):
def evalRPN(self, tokens):
"""
:type tokens: List[str]
:rtype: int
"""
from collections import deque
def cal(data_1,data_2,item):
if item == '/':
return abs(data_2) // abs(data_1) *(-1 if (data_2 > 0) ^ (data_1 > 0) else 1)
elif item == '+':
return data_2 + data_1
elif item == '-':
return data_2 - data_1
else:
return data_2 * data_1
dq = deque()
calset = ['/','+','-','*']
for item in tokens:
if item in calset:
#print('if')
data_1 = dq.pop()
data_2 = dq.pop()
data = cal(int(data_1),int(data_2),item)
dq.append(data)
else:
#print('else')
dq.append(item)
#print(dq)
return dq[0]
参考:
#https://www.cnblogs.com/zuoyuan/p/3760530.html 注意负数的除法,c++和pytho的区别
class Solution:
# @param tokens, a list of string
# @return an integer
def evalRPN(self, tokens):
stack = []
for i in range(0,len(tokens)):
if tokens[i] != '+' and tokens[i] != '-' and tokens[i] != '*' and tokens[i] != '/':
stack.append(int(tokens[i]))
else:
a = stack.pop()
b = stack.pop()
if tokens[i] == '+':
stack.append(a+b)
if tokens[i] == '-':
stack.append(b-a)
if tokens[i] == '*':
stack.append(a*b)
if tokens[i] == '/':
if a*b < 0:
stack.append(-((-b)/a))
else:
stack.append(b/a)
return stack.pop()
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