Uncompress a String, repeat chars `n` times

Question

I have the following problem statement:

Write a function, uncompress, that takes in a string as an argument. The input string will be formatted into multiple groups according to the following pattern:

number + char

for example, '2c' or '3a'.

The function should return an uncompressed version of the string where each 'char' of a group is repeated 'number' times consecutively. You may assume that the input string is well-formed according to the previously mentioned pattern.

test_00: uncompress("2c3a1t"); // -> 'ccaaat'

Here is my code which is using a stack. The problem is that it's only returning 'cc' and I can't figure out why. I've console logged what goes into the IF ELSE and I'm hitting both so I don't understand why nothing gets pushed to the stack.

Would really appreciate the help if someone can spot what I'm missing.

const uncompress = (s) => { 
  const nums = '23456789';
  const stack = []; 
  for (let char of s) {
    if (nums.includes(char)) {
      stack.push(Number(char));
    } else {
      const num = stack.pop();
      stack.push(char.repeat(num));
    };
  };
  return stack.join('');
};

console.log(uncompress("2c3a1t")); // -> 'ccaaat'

I've added a snippet; it would be helpful if you could add examples showing inputs and expected outputs, along with what your function outputs. E.g., `console.log(uncompress('2c3a1t')); // 'ccaaat'`. — Heretic Monkey, Jan 20 '22 at 18:55
Your code should be fine, you're just missing `1` in your `nums`; — McAden, Jan 20 '22 at 22:29

Luca Kiebel · Answer 1 · 2022-01-20T19:18:11.937

1

Here's how I would do it:

Split the string up into pairs of numbers and chars:

str.match(/\d+[a-zA-Z]/g)

And reduce that array to a string, while taking each value from the array, getting the char from it (cv.match(/[a-zA-Z]/)[0]) and repeating it according to the number (.repeat(parseInt(cv)))

const uncompress = str => str.match(/\d+[a-zA-Z]/g).reduce((acc, cv) =>
  acc + cv.match(/[a-zA-Z]/)[0].repeat(parseInt(cv)), "")

console.log(uncompress("2c3a1t"))
console.log(uncompress("27b1d8g"))

edited Jan 20 '22 at 19:18

answered Jan 20 '22 at 19:11

Luca Kiebel

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I love regex answers. Is there anything regex can't solve? – Trevor Jan 20 '22 at 19:20
@Trevor X/HTML is a big one, well, and other problems that deal with non-regular languages :P (https://stackoverflow.com/a/1732454/6634591) – Luca Kiebel Jan 20 '22 at 19:21
What happens when you need to regex a non Latin based language? – Trevor Jan 20 '22 at 19:25
https://stackoverflow.com/questions/21109011/javascript-unicode-string-chinese-character-but-no-punctuation – Luca Kiebel Jan 20 '22 at 19:26
That makes my eyes water. You regex experts are a cut above. – Trevor Jan 20 '22 at 19:34

score 0 · Answer 2 · answered Jan 20 '22 at 19:04

And just like that I was able to write the code which passed the test case:

  const nums = '123456789';
  const stack = []; 
  for (let char of s) { 
    if (nums.includes(char)) {
      stack.push(Number(char));
    } else {
      let num = '';
      while (nums.includes(stack[stack.length - 1])) {
        num += stack.pop(); 
      }
      stack.push(char.repeat(num));
    };
  };
  return stack.join('');
};

Uncompress a String, repeat chars `n` times

2 Answers2