38. Count and Say

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, 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"

Solution:

var countAndSay = function(n) {
  var result = "1";
    for(var i = 1; i < n; i++) {
        var count = 0;
        var tmp = "";
        var prev = result[0];
        for(var j = 0; j <= result.length; j++) {
            if(j === result.length || result[j] !== prev) {
                tmp += count + prev;
                count = 1;
                prev = result[j];
            }
            else {
                count++;
            }
        }
        result = tmp;
    }
    return result;
};

JavaScript 字符串拼接：
var result = charA + charB;
Note: 在旧版本的浏览器，字符串拼接可能存在效率问题，但IE5之后的浏览器都修复了这个问题。