25期代码随想录算法训练营第十天

算法训练营第十天"/>

25期代码随想录算法训练营第十天

目录

• 20. 有效的括号
• 1047. 删除字符串中的所有相邻重复项
• 150. 逆波兰表达式求值

20. 有效的括号

链接

class Solution:def isValid(self, s: str) -> bool:closeToOpen = {")": "(", "]":"[", "}":"{"}stack = []for string in s:if string not in closeToOpen:stack.append(string)else:if not stack or stack.pop() != closeToOpen[string]:return Falsereturn len(stack) == 0

1047. 删除字符串中的所有相邻重复项

链接

class Solution:def removeDuplicates(self, s: str) -> str:stack = []for string in s:if not stack:stack.append(string)else:if string == stack[-1]:stack.pop()else:stack.append(string)return ''.join(stack)

150. 逆波兰表达式求值

链接

from operator import add, mul, sub
class Solution:def evalRPN(self, tokens: List[str]) -> int:stack = []op_map = {"+": add, "-": sub, "*": mul, "/": lambda x,y: int(x/y)}for token in tokens:if token not in op_map:stack.append(token)else:y = int(stack.pop())x = int(stack.pop())res = op_map[token](x, y)stack.append(res)return int(stack[-1])