Leetcode 38: Count and Say

Posted 2020-10-13 Keep walking

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, generate the nth 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"


Notes: should ask clarify question what is after 4, I was confused by the example input where I thought we only need to count dup 1s.

 1 public class Solution {
 2     public string CountAndSay(int n) {
 3         var result = "1";
 4         
 5         while (n-- > 1)
 6         {
 7             var sb = new StringBuilder();
 8             
 9             int i = 0;
10             while (i < result.Length)
11             {
12                 int j = i + 1;
13                 while (j < result.Length && result[i] == result[j])
14                 {                
15                     j++;
16                 }
17                 
18                 sb.Append(j - i);
19                 sb.Append(result[i]);
20                 i = j;
21             }
22             
23             result = sb.ToString();
24         }
25         
26         return result;
27     }
28 }