leetcode 241. Differ

发布时间：2019-08-27 08:03:04编辑：auto阅读（1455）

    题目：

    Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are+, - and *.

    大意是给定一个运算，求解所有运算序列的解

    例如

    Input: "2*3-4*5"

    (2*(3-(4*5))) = -34
((2*3)-(4*5)) = -14
((2*(3-4))*5) = -10
(2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10

    Output: [-34, -14, -10, -10, 10]

    算法思路：

    将运算转换成栈过程，这样就将问题转换成一个递归问题

    即每一步分为两种走法：

        1）继续向栈中添加数字与运算符

        2）弹出2个数字1个运算符进行计算


    代码：

    class Solution(object):
    def addOperatorAndNumber(self, inputList, stack):
        if len(inputList) < 2:
            return []
        stack.append(inputList[0])
        stack.append(inputList[1])

        inputList = inputList[2:]
        return self.calculate(inputList,stack)

    def calculateTopStack(self, inputList, stack):
        number1 = int(stack.pop())
        operator = stack.pop()
        number2 = int(stack.pop())

        if operator == "+":
            stack.append(number1 + number2)
        elif operator == "-":
            stack.append(number2 - number1)
        elif operator == "*":
            stack.append(number1 * number2)

        return self.calculate(inputList,stack)

    def calculate(self, inputList, stack):
        if len(stack) == 1:
            if len(inputList) == 0:
                return [stack[0]]
            else:
                return self.addOperatorAndNumber(inputList,stack)

        result1 = self.calculateTopStack(inputList[:], stack[:])
        result2 = self.addOperatorAndNumber(inputList[:],stack[:])

        result1.extend(result2)
        return result1

    def diffWaysToCompute(self, input):
        """
        :type input: str
        :rtype: List[int]
        """

        input = input.replace('+'," + ")
        input = input.replace("-"," - ")
        input = input.replace("*"," * ")

        inputList = input.split(" ")
        stack = [int(inputList[0])]
        return  self.calculate(inputList[1:],stack)




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