LeetCode 38 - Count and Say

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

public String countAndSay(int n) {

        if (n < 0)

            return "";

        // Go n-1 steps starting from the first integer "1"

        String result = "1";

        for (int i = 1; i < n; i++) {

            // StringBuilder: a mutable sequence of characters similar to StringBuffer

            // but with no guarantee of synchronization; recommended for most cases

            StringBuilder builder = new StringBuilder();

            int count = 1;      // The number of appearances of the same digit

            for (int j = 1; j < result.length(); j++) {

                if (result.charAt(j) == result.charAt(j-1)) {   // Same as the preceding digit

                    count++;

                } else {        // A different digit

                    builder.append(count);      // Append the count of appearances of the character

                    builder.append(result.charAt(j-1));     // Append the character itself

                    count = 1;      // Reset count

                }

            }

            // The last digit and its count of appearances have not been included in builder

            builder.append(count);

            builder.append(result.charAt(result.length()-1));

            // Get the next integer in the sequence

            result = builder.toString();

        }

        // Out of loop; we arrive at the n-th integer

        return result;

    }

http://tech-wonderland.net/blog/leetcode-count-and-say.html

public String countAndSay(int n) {

03	if (n < 1)

04	return "";

05	StringBuffer strBuffer = new StringBuffer("1");

06	while (--n > 0) {

07	int i = 0;

08	int j = 0;

09	int len = strBuffer.length();

10

11	StringBuffer strNext   = new StringBuffer();

12	while (j < len) {

13	while (j < len &&

14	(j == i || strBuffer.charAt(j) == strBuffer.charAt(j-1)))

15

++j;

16

17	strNext.append(j - i);

18	strNext.append(strBuffer.charAt(i));

19

i = j;

20

}

21	strBuffer = strNext;

22

}

23

24	return strBuffer.toString();

25

}

Look-and-Say Sequence - GeeksforGeeks

// Returns n'th term in look-and-say sequence

string countnndSay(int n)

{

    // Base cases

    if (n == 1)      return "1";

    if (n == 2)      return "11";

    // Find n'th term by generating all terms from 3 to

    // n-1.  Every term is generated using previous term

    string str = "11"; // Initialize previous term

    for (int i = 3; i<=n; i++)

    {

        // In below for loop, previous character

        // is processed in current iteration. That

        // is why a dummy character is added to make

        // sure that loop runs one extra iteration.

        str += '$';

        int len = str.length();

        int cnt = 1; // Initialize count of matching chars

        string  tmp = ""; // Initialize i'th term in series

        // Process previous term to find the next term

        for (int j = 1; j < len; j++)

        {

            // If current character does't match

            if (str[j] != str[j-1])

            {

                // Append count of str[j-1] to temp

                tmp += cnt + '0';

                // Append str[j-1]

                tmp += str[j-1];

                // Reset count

                cnt = 1;

            }

            //  If matches, then increment count of matching

            // characters

            else cnt++;

        }

        // Update str

        str = tmp;

    }

    return str;

}

http://rleetcode.blogspot.com/2014/02/count-and-say-java.html

	public String countAndSay(int n) { // Start typing your Java solution below
	// DO NOT write main() function
	if (n<=1){
	return String.valueOf(1);
	}
	else{
	return say(countAndSay(n-1));
	}
	}
	private String say(String s){
	int i=0;
	int count=1;
	StringBuffer sb=new StringBuffer();
	while(i<s.length()){
	int j=i+1;
	while(j<s.length()&&s.charAt(j)==s.charAt(i)){
	count++;
	j++;
	}
	sb.append(count);
	sb.append(s.charAt(i));
	i=j;
	count=1;
	}
	return sb.toString();
	}

https://gist.github.com/Kevin-Lee/3678544
http://rosettacode.org/wiki/Look-and-say_sequence#Java
Read full article from LeetCode - Count and Say | Darren's Blog