38.count-and-say.js

/*
 * @lc app=leetcode id=38 lang=javascript
 *
 * [38] Count and Say
 */
/**
 * @param {number} n
 * @return {string}
 */
/*
Question
represent a number by a string

1=>1
2=>11
3=>21
4=>1211
5=>111221

Rule

*/

var countAndSay = function(n) {
  var hash = {};
  hash[1] = "1";

  var hashPos;
  for (var i = n; i >= 1; i--) {
    if (hash[i]) hashPos = i;
  }

  var str = hash[hashPos];
  for (var i = hashPos + 1; i <= n; i++) {
    var _str = "";
    var target = "";
    var num = 0;
    for (var j = 0, len = str.length; j < len; j++) {
      if (target === "") (target = str[j]), (num = 1);
      else if (str[j] === target) num++;
      else {
        _str += num + target;
        target = str[j];
        num = 1;
      }
    }

    if (num) _str += num + target;
    str = _str;

    hash[i] = str;
  }

  return str;
};