0038. Count and Say.js

// The count-and-say sequence is the sequence of integers with the first five terms as following:

// 1.     1
// 2.     11
// 3.     21
// 4.     1211
// 5.     111221
// 1 is read off as "one 1" or 11.
// 11 is read off as "two 1s" or 21.
// 21 is read off as "one 2, then one 1" or 1211.

// Given an integer n where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.

// Note: Each term of the sequence of integers will be represented as a string.

// Example 1:

// Input: 1
// Output: "1"

// Example 2:

// Input: 4
// Output: "1211"


/**
 * @param {number} n
 * @return {string}
 */
var countAndSay = function(n) {
  let res = '1'
  const say = s => {
    let res = "";
    let count = 0;
    let num = s[0];
    for (let i = 0; i < s.length; i++) {
      if (s[i] === num) {
        count++;
      } else {
        res += count + s[i - 1];
        count = 1;
        num = s[i];
      }
    }
    return res + count + num;
  };
  for (let i = 1; i < n; i++) {
    res = say(res)
  }
  return res
}
// Runtime: 48 ms, faster than 97.26% of JavaScript online submissions for Count and Say.
// Memory Usage: 35.8 MB, less than 33.33% of JavaScript online submissions for Count and Say.