38.count-and-say.java

/*
 * @lc app=leetcode id=38 lang=java
 *
 * [38] Count and Say
 *
 * https://leetcode.com/problems/count-and-say/description/
 *
 * algorithms
 * Easy (39.56%)
 * Total Accepted:    271K
 * Total Submissions: 677.5K
 * Testcase Example:  '1'
 *
 * 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 where 1 ≤ n ≤ 30, generate the n^th 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"
 *
 */
class Solution {
  public String countAndSay(int n) {
    String result = "1";
    for (int i = 1; i < n; i++) {
      StringBuilder sb = new StringBuilder();
      int len = result.length();
      int count = 1;
      int j = 1;
      for (; j < len; j++) {
        if (result.charAt(j) != result.charAt(j-1)) {
          sb.append(count).append(result.charAt(j-1));
          count = 1;
        } else {
          count++;
        }
      }
      sb.append(count).append(result.charAt(j-1));
      result = sb.toString();
    }
    return result;
  }
}