codewar代码练习1——8级晋升7级

最近发现一个不错的代码练习网站codewar（http://www.codewars.com）。注册了一个账号，花了几天的茶余饭后时间做题，把等级从8级升到了7级。本文的目的主要介绍使用感受及相应题目，可供大家参考。

新人注册为8级，入门题NO.1:

topic: Multiply

instructions:The code does notexecute properly. Try to figure out why.

my solution:

def multiply(a, b):
    c = a * b
    return c

NO2:

topic: ListFiltering

instruction:In this kata you will create a function that takes a list of non-negative integers and strings and returns a new list with the strings filtered out. 

example:

my solution:

def filter_list(l):
    new_l =[]
    for x in l:
        if type(x) != str:
            new_l.append(x)
    return new_l

best practice from others：

def filter_list(l):
  'return a new list with the strings filtered out'
  return [i for i in l if not isinstance(i, str)]

and

def filter_list(l):
  'return a new list with the strings filtered out'
  return [x for x in l if type(x) is not str]

No.3

topic：two to one

instruction：Take 2 strings s1 and s2 including only letters from ato z. Return anew sorted string, the longest possible, containing distinct letters,each takenonly once - coming from s1 or s2.

Examples: 

``` a = "xyaabbbccccdefww" b ="xxxxyyyyabklmopq" longest(a, b) -> "abcdefklmopqwxy"

a = "abcdefghijklmnopqrstuvwxyz" longest(a, a) ->"abcdefghijklmnopqrstuvwxyz" ```

my solution:

import string
from pandas import Series
def longest(a,b):
    c1 = a + b
    c2 = list(c1)
    c3 = Series(c2)
    c4 = c3.unique().tolist()
    c5 = sorted(c4)
    c6 = ''.join(c5)
    return c6

best solution from others:

def longest(a1, a2):
    return "".join(sorted(set(a1 + a2)))

No.4

topic:Categorize New Member

instruction:The Western Suburbs Croquet Club has two categories of membership,Senior and Open. They would like your help with an application form that willtell prospective members which category they will be placed.

 To be a senior, a member must be at least 55 years old and have ahandicap greater than 7. In this croquet club, handicaps range from -2 to +26;the better the player the lower the handicap.

example：

my solution:

def openOrSenior(data):
    a = []
    for i in data:
        if i[0]>54 and i[1]>7:
            a.append('Senior')
        else:
            a.append('Open')
    return a

best solution from others:

def openOrSenior(data):
  return ["Senior" if age >= 55 and handicap >= 8 else "Open" for (age, handicap) in data]

No.5

topic: Array.diff

instruction:your goal in this kata is to implement an difference function, which subtracts one list from another.

example:

my solution:

def array_diff(a, b):
    diff = []
    for i in a:
        if i not in b:
            diff.append(i)
    return diff

best solution from others:

def array_diff(a, b):
    return [x for x in a if x not in b]

No.6

topic:Mumbling

instruction:This time no story, no theory.

example:

my solution:

def accum(s):
    b = list(s)
    i = 0
    for j in b:
        b[i] = b[i] * (i+1)
        i = i+1
    a = list(map(lambda x: x.capitalize(),b))
    c = '-'.join(a)
    return c

best solution from others:

def accum(s):
    return '-'.join((a * i).title() for i, a in enumerate(s, 1))

No.7

topic:Multiples of 3 or 5
instruction:If we list all the natural numbers below 10 that are multiples of 3or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.Finish the solution so that it returns the sum of all the multiplesof 3 or 5 below the number passed in.

note:If the number is a multiple of both 3 and 5, only count it once.

my solution:

def solution(number):
    a = []
    j = 3 
    while j<number:
        if j%3==0 or j%5==0:
            a.append(j)
        j = j + 1
    return sum(a)

best solution from others:

def solution(number):
    return sum(x for x in range(number) if x % 3 == 0 or x % 5 == 0)

在8级的时候，做7级题甚至6级题，能快速升级到7级。知识点总结：

1. type和instance判断数据类型

2. 遍历list的方法，list切片知识，如何读取两个list中的非交集

3. str转list，list转series数据，array转list（array.tolist（）），字母如何排序（sorted）

4. set 函数（创建一个无序不重复元素集）

5. 改变字符串的首字母：capital，upper，lower，title

6. join连接字符，split分割字符串

7. 枚举函数enumerate，例如枚举list中的索引和元素

8. 如何跳出嵌套循环（写个def，用return）

9. try和except的使用

10. lambda函数使用

感受：

8级到7级的晋升路上，主要涉及的python的数据结构相关的基础知识点。而python的数据结构知识是在一年前学习的，零零落落已经忘得差不多了，做题目的时候基本靠谷歌知识点。在codewar做题的时候，貌似答案没有通过，是无法看到其他人的答案的。在通过答案后，再看其他人的解法，常常有眼前一亮的感觉。