38. Count and Say徒手尝试#2(Done)

Solution

public class Solution {    public String countAndSay(int n) {        if (n < 1) {            throw new IllegalArgumentException("Illegal argument for function countAndSay.");        }        String s = "1";        while (--n > 0) {            StringBuilder tmp = new StringBuilder();            int i = 0, j = 0;            while (j < s.length()) {                if (s.charAt(j) != s.charAt(i)) {                    tmp.append(j - i);                    tmp.append(s.charAt(i));                    i = j;                }                j++;            }            tmp.append(j - i);            tmp.append(s.charAt(i));            s = tmp.toString();        }        return s;    }}

Problem#1
* String未初始化
* 注意不同类型之间不能随便转换
* char如何转成int
* 什么时候应当将String转换成charArray()