08 13 哔哩哔哩 笔试 后端开发 Python

分析

30道选择题，3道编程题105分钟，编程题简单，重点还是选择

1

给定四个数值，判断能不能经过加减乘除运算得到24.

• 回溯，中间遇到的坑：不能直接对遍历的操作使用eval，有运算符的优先级问题

#
# 
# @param arr int整型一维数组 
# @return bool布尔型
#
class Solution:
    def Game24Points(self , arr ):
        # write code here
        visited = [0] * 4
        def helper(visited,s):
            if sum(visited) == 4:
                ss = s.copy()
                res = ss.pop(0)
                #计算结果是不是24
                while ss:
                    res = eval(str(res)+ss.pop(0))
                if res == 24:
                    return True
                return False
            #回溯
            for i in range(len(arr)):
                if not visited[i]:
                    for symbol in ['+','-','*','/']:
                        s.append(symbol+str(arr[i]))
                        visited[i] = 1
                        if helper(visited,s):
                            return True
                        visited[i] = 0
                        s.pop()
            return False
        for i in range(len(arr)):
            visited[i] = 1
            if helper(visited,[str(arr[i])]):
                return True
            visited[i] = 0
        return False

a = Solution()
print(a.Game24Points([7,2,1,10]))

2.

字符串匹配 easy题

class Solution:
    def IsValidExp(self , s ):
        # write code here
        q_map = {')':'(',']':'[','}':'{'}
        if not s:return True
        stack = []
        for i in range(len(s)):
            if s[i] not in q_map.keys():
                stack.append(s[i])
            elif not stack:return False
            elif q_map[s[i]] != stack.pop():
                return False
        if not stack:return True
        return False

a = Solution()

print(a.IsValidExp('{{}}}'))

3

换零钱，贪心。easy题

class Solution:
    def GetCoinCount(self , N ):
        # write code here
        vals = [64,16,4,1]
        money = 1024 - N
        res = 0
        for val in vals:
            cur_cnt = money // val
            money -= cur_cnt * val
            res += cur_cnt
        return res

总结

拼选择题和学历的时候到了[Dog]