Given a character sequence and a defined document unit, tokenization is the task of chopping it up into pieces, called tokens , perhaps at the same time throwing away certain characters, such as punctuation. (ref)

For tasks of string processing, in many cases we are given a string, and are asked to understand this string in specific logic and then return the result.

For example, if we are to calculate the result of following expression:

 1 * (20 -   300      )

before we implement the logic, first we need to get the "keywords"(tokens) and ignore the spaces, like following:

'1','*', '(', '20', '-', '300', ')'

Then we can process above tokens and get the result easier.

You are asked to implement a tokenize() for arithmetic expression , which works as below:

const tokens = tokenize(' 1 * (20 -   300      ) ')


while (true) {
  let token = tokens.next()
  if (token.done) {
    break
  }
  console.log(token.value)
}

or you can use for ... of

for (let token of tokens) {
    console.log(token)   
}

Because it is trivial, in a real interview you talk to interviewer and implement tokenizer later, this could save yourself some time for more important tasks.

Input

input only contains valid non-negative integers with +, -, *, /, (, ) and spaces, space should be ignored.
your method should return an Generator object.

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119. create a tokenizer