Codewars Challenge - The Deaf Rats of Hamelin - JavaScript - 如何按特定字符集拆分字符串？

Question

Link to challenge

Essentially, the idea is that if a rat - O~ - is facing the Piper - P - then it's going the correct way.

Here is a rat going left: O~

Here is a rat going right: ~O

We want to count how many 'deaf rats' exist in a string - how many are facing the wrong way.

Here, there is 1 deaf rat: PO~ O~ ~OO~

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My logic is to first check for if the Piper is on the left or right side of the string.

If he's not, then we need to split the string based on where the Piper is located in the string, and then count how many rats on the left side are not facing him, and how many rats on the right side are not facing him.

 var countDeafRats = function(town) { town = town.replace(/[ ]/g, ''); let deafCount = 0; //if piper's on the left if (town[0] === 'P') { for (let i = 0; i < town.length; i++) { if (town[i] === '~O') { deafCount ++; } } } //if piper's on the right if (town[town.length - 1] === 'P') { for (let j = 0; j < town.length; j++) { if (town[j] === 'O~') { deafCount ++; } } } let rats = town.split('P'); console.log('ratssss', rats); let leftRats = []; let rightRats = []; return deafCount; } console.log(countDeafRats("~O~OP ~O~O"));

In the case above, here is the array of rats: [ '~O~O', '~O~O' ] So there are two rats on the right side that are going the wrong way (deaf rats).

What I'd like to do, is to push the left and right rats into their own arrays, and then count the deaf rats in each individual array.

But I'm not able to split the string ~O~O by either ~O or O~ .

I would like to get ['~O', '~O'] for the leftRats and ['~O', '~O'] for the rightRats .

I had tried:

leftRatsssss [ [ '', '', '' ] ]
rightRatssss [ [ '~', 'O' ] ]

But it's doing something very different from what was expected:

 leftRatsssss [ [ '', '', '' ] ] rightRatssss [ [ '~', 'O' ] ]

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Split is not splitting the string by the string given as a parameter. So that's the real point of my question, then - how can you split a string by a certain set of characters?

Ie If I wanted to split the string 'the' by 'he' , I'd want 'the' to become ['t', 'he'] - I've tried regex for this case?

 console.log("the".split(/[he]/gi));

And it seems to be doing the opposite of what I want. Any suggestions, then, for splitting a string by a given set of characters?

Answer 1

You can split the string by the P regardless, then turn each segment (on the left and right of the P ) into an array of each 2-character chunk. Eg ~O~OP ~O~O turns into ['~O', '~O'] for the left chunk, and ['~O', '~O'] for the right chunk. Then count up the number of occurrences of O~ in the first chunk, and the number of occurrences of ~O in the second chunk:

 var countDeafRats = function(town) { const [leftRats, rightRats] = town .replace(/[^O~P]/g, '') .split('P') .map(segment => segment.match(/.{2}/g) || []); return ( leftRats.reduce((a, rat) => a + (rat === 'O~'), 0) + rightRats.reduce((a, rat) => a + (rat === '~O'), 0) ); } console.log(countDeafRats("~O~OP ~O~O"));