38 Count and Say

he 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

1is read off as"one 1"or11.
11is read off as"two 1s"or21.
21is read off as"one 2, thenone 1"or1211.

Given an integern, generate thenthterm 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)

class Solution {
    public String countAndSay(int n) {
        if (n <= 0) return "";
        String s = "1";
        for (int i = 1; i < n; i++) {
            StringBuffer sb = new StringBuffer();
            int count = 1;
            for (int j = 0; j < s.length(); j++) {
                if (j < s.length()-1) {
                    if (s.charAt(j) == s.charAt(j+1)) count++;
                    else {
                        sb.append(String.valueOf(count)+s.charAt(j));
                        count = 1;
                    }
                } else 
                    sb.append(String.valueOf(count)+s.charAt(j));
            }
            s = sb.toString();
        }
        return s;
    }
}

public class Solution {
    public String countAndSay(int n) {
        String s = "1";
        for (int i = 1; i < n; i++) {
            StringBuilder sb = new StringBuilder();
            for (int j = 1, count = 1; j <= s.length(); j++) {
                if (j == s.length() || s.charAt(j - 1) != s.charAt(j)) {
                    sb.append(count);
                    sb.append(s.charAt(j - 1));
                    count = 1;
                } else count++;
            }
            s = sb.toString();
        }
        return s;
    }
}