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Conway's Look and Say - Generalized

5 kyu
Description

Your task is to create a function that will take an integer and return the result of the look-and-say function on that integer. This should be a general function that takes as input any positive integer, and returns an integer; inputs are not limited to the sequence which starts with "1".

Conway's Look-and-say sequence goes like this:

Start with a number. Look at the number, and group consecutive digits together. For each digit group, say the number of digits, then the digit itself. This can be repeated on its result to generate the sequence.

For example:

  • Start with 1.
  • There is one 1 --> 11
  • Start with 11. There are two 1 digits --> 21
  • Start with 21. There is one 2 and one 1 --> 1211
  • Start with 1211. There is one 1, one 2, and two 1s --> 111221

Sample inputs and outputs::

  • 0 --> 10
  • 2014 --> 12101114
  • 9000 --> 1930
  • 22322 --> 221322
  • 222222222222 --> 122

解題思路​

function lookSay(number) {
  const numStr = number.toString();
  let result = "";
  let count = 1;

  for (let i = 0; i < numStr.length; i++) {
    // 如果下一個數字跟現在的一樣，就累加
    if (numStr[i] === numStr[i + 1]) {
      count++;
    } else {
      // 否則就把目前的統計加進結果字串
      result += count.toString() + numStr[i];
      count = 1; // 重置計數
    }
  }

  return parseInt(result, 10); // 轉成數字回傳
}

心得​

不使用 Object 的 Counter，而是簡化為一個數字。