代码随想录算法训练营第十天| 第五章 栈与队列part02

今天的三道题仍然是关于栈与队列，三道题都还算比较常规

直接贴代码咯

第一道： 20. 有效的括号

class Solution:
    def isValid(self, s: str) -> bool:
        ## 使用栈和队列
        stack = []
        s = list(s)
        for i in s:
            if i == "{" or i == "[" or i == "(":
                stack.append(i)
            else:
                if len(stack) == 0:
                    return False
                a = stack.pop()
                if i == "]" and a != "[":
                    return False
                if i == "}" and a != "{":
                    return False   
                if i == ")" and a != "(":
                    return False
        if len(stack) != 0:
            return False
        return True
 
 
 
 

第二道：1047. 删除字符串中的所有相邻重复项

class Solution:
    def removeDuplicates(self, s: str) -> str:
        stack = []
        s = list(s)
        for i in s:
            if  stack == [] or stack[-1] != i:
                stack.append(i)
            else:
                stack.pop()
        return "".join(stack)

第三道：150. 逆波兰表达式求值

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        stackNum = []
        for i in tokens:
            if i[0] == '-' and i[1:].isdigit():
                stackNum.append(i)
            elif i.isdigit():
                stackNum.append(i)
            else:
                temp1 = int(stackNum.pop())
                temp2 = int(stackNum.pop())
                if i == "+":
                    stackNum.append(temp2+temp1)
                if i == "-":
                    stackNum.append(temp2-temp1)
                if i == "*":
                    stackNum.append(temp2*temp1)
                if i == "/":
                    if temp2//temp1 < 0:
                        if temp2//temp1 == temp2 / temp1:
                            stackNum.append(temp2//temp1)
                        else:
                            stackNum.append(temp2//temp1 + 1)
                    else:
                        stackNum.append(temp2//temp1)
        return int(stackNum[0])