CodeWars 刷题总结

CodeWars

Base Conversion

In this kata you have to implement a base converter, which converts positive integers between arbitrary bases / alphabets. Here are some pre-defined alphabets:

bin      = '01'
oct      = '01234567'
dec      = '0123456789'
hex      = '0123456789abcdef'
allow    = 'abcdefghijklmnopqrstuvwxyz'
allup    = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
alpha    = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
alphanum = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

The function convert() should take an input (string), the source alphabet (string) and the target alphabet (string). You can assume that the input value always consists of characters from the source alphabet. You don't need to validate it.

Examples

convert("15", dec, bin)       ==>  "1111"
convert("15", dec, oct)       ==>  "17"
convert("1010", bin, dec)     ==>  "10"
convert("1010", bin, hex)     ==>  "a"
convert("0", dec, alpha)      ==>  "a"
convert("27", dec, allow)     ==>  "bb"
convert("hello", allow, hex)  ==>  "320048"

Additional Notes:

The maximum input value can always be encoded in a number without loss of precision in JavaScript. In Haskell, intermediate results will probably be too large for Int.
The function must work for any arbitrary alphabets, not only the pre-defined ones
You don't have to consider negative numbers

知识点

• 这个题目的关键是利用十进制数字和二进制数字转换的模式，先把输入的字符串转换为数字，如'123'，则为((1*10) + 2)*10 + 3, 如input为'abc'，source为allow时，a对应的index为0，b为1，c为2，则对应的数字为(0*26 + 1)*26 + 2
• 然后再把数字转换为输出的进制格式