38. Count and Say

QUESTION:

The count-and-say sequence is the sequence of integers beginning as follows: 1, 11, 21, 1211, 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 sequence.

Note: The sequence of integers will be represented as a string.

EXPLANATION:

其实只要理解了题目的意思也是很好解决的。

1.当是1的时候就是1，2的时候是1个1，3的时候是2个1，4的时候1个2和1个1

2.所以直接选择循环，循环到n，数出所有的数就可

SOLUTION:

public class Solution {
    public String countAndSay(int n) {
        int i = 2;
        String result = "1";
        StringBuilder builder;
        while (i<=n){
            builder = new StringBuilder();
            char[] chars = result.toCharArray();
            char pre = chars[0];int count =0;
            for(char ch:chars){
                if(ch==pre){
                    count++;
                }else{
                    builder.append(count);
                    builder.append(pre);
                    pre = ch;
                    count = 1;
                }
            }
            i++;
            builder.append(count);
            builder.append(pre);
            result = builder.toString();
        }
        return result;
    }
}
>
--> return <--