class Solution:
def romanToInt(self, s):
"""
:type s: str
:rtype: int
"""
numDict = {'I':1, 'V':5, 'X':10, 'L':50, 'C':100, 'D':500, 'M':1000}
res = numDict.get(s[-1])
for i in range(0, len(s)-1):
if (numDict[s[i]] < numDict[s[i+1]]):
res -= numDict.get(s[i])
else:
res += numDict.get(s[i])
return res
# 使用Solution2的思路，纵向对比strs每个字符是否相同
class Solution:
def longestCommonPrefix(self, strs):
"""
:type strs: List[str]
:rtype: str
"""
if not strs: #str is empty
return ""
for i, letter_vertical in enumerate(zip(*strs)): #i_max == the shortest length of strs
if len(set(letter_vertical)) > 1:
return strs[0][:i]
return min(strs)
class Solution:
def isValid(self, s):
"""
:type s: str
:rtype: bool
"""
stack = []
opDict = {"]":"[", "}":"{", ")":"("}
for char in s:
if char in opDict.values():
stack.append(char)
elif char in opDict.keys():
if stack == [] or opDict[char] != stack.pop(): # pop 移除并返回List最后一个元素
return False
else:
return False
return stack == [] # 全部匹配完
