codefights arcade The Core task 22

swapAdjacentBits
https://codefights.com/arcade/code-arcade/corner-of-0s-and-1s/dShYZZT4WmvpmfpgB

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algorithm 1, 2, and 3
using a regular expression to find and replace all pairs of bits

topics:
- different ways to use the string `.replace` method (using string arguments, or using regexp and function arguments, doing a replaceAll)
- padding function (concatenates leading zeros onto binary strings of length less than 32)
- avoiding repetition by assigning a variable inline, or invoking a function inline
- using `Math.log2` to find the length of the binary string
- you can basically use a js object like a switch (like a pairwise mapping of input and output values)
- weird issue with arrow functions: if you wanna just return an object (or at least something beginning with the `{` character), you need to wrap it in parentheses (otherwise it'll be looking for a return statement)


algorithm 4 and 5
using a mask for just the odd bits and shifting them left by 1, then using a mask for the even bits and shifting right by 1, then putting them back together

topics:
- review of decimal to binary conversion
- binary integer literals (beginning with `0b`), and hexadecimal (beginning with `0x`), or we could just use decimal (main point is that we can use different representations for the same value)
- since the bits in each part are mutually exclusive in this case, we can either use `|` or `+` to put them together