Count and Say LeetCode Solution

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.

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

Link: https://leetcode.com/problems/count-and-say/

Solution #

class Solution { public: string countAndSay(int n) {

    // base case
    if(n == 1) {
        return "1";
    }
    
    string result = "1";
    
    for(int i=2;i<=n;i++) {
        char previous = result\[0\];
        string temp = "";
        int count = 1;
        
        for(int j=1;j<=result.length();j++) {
            if(result\[j\] != previous) {
                temp = temp + to\_string(count) + previous;
                previous = result\[j\];
                count = 1;
            }else{
                count++;
            }
        }
        result = temp;
    }
    
    return result;
}

};