Count and Say

Problem Statement - link #

The count-and-say sequence is a sequence of digit strings defined by the recursive formula:

• countAndSay(1) = "1"
• countAndSay(n) is the way you would “say” the digit string from countAndSay(n-1), which is then converted into a different digit string.

To determine how you “say” a digit string, split it into the minimal number of groups so that each group is a contiguous section all of the same character. Then for each group, say the number of characters, then say the character. To convert the saying into a digit string, replace the counts with a number and concatenate every saying.

For example, the saying and conversion for digit string "3322251":

Given a positive integer n, return the nth term of the count-and-say sequence.

Examples #

Example 1:

Input: n = 1
Output: "1"
Explanation: This is the base case.

Example 2:

Input: n = 4
Output: "1211"
Explanation:
countAndSay(1) = "1"
countAndSay(2) = say "1" = one 1 = "11"
countAndSay(3) = say "11" = two 1's = "21"
countAndSay(4) = say "21" = one 2 + one 1 = "12" + "11" = "1211"

Constraints #

• 1 <= n <= 30

Solutions #

class Solution {
public:
    string countAndSay(int n) {
      int i=1;
      string res="1";
      
      while(n-1) {
         string temp = "" ; 
         char c = res[0];
         int k = 0;
        
         for(int i=0; i<res.size(); i++){
           if(c==res[i]) k++;
           else {
               temp = temp + to_string(k) + c;      
                k = 1;
                c = res[i];
            }
         }
        
        if(k) temp = temp + to_string(k) + c;      
        res = temp;
        
         n--;
       } 
      return res;
    }
};