(Leet Code JS)Count and Say

38. Count and Say

 

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

 

같은 문자가 연속적인지 카운팅을 한 후 카운팅 결과와 문자를 합해 answer을 갱신해주면 된다.

/**
 * @param {number} n
 * @return {string}
 */
const countAndSay = (n) => {
    let answer = "1";
    
    for(let i = 2; i <= n; i++){
        let count = 1;
        let before = answer[0];
        let string = "";
        
        for(let j = 1; j < answer.length; j++){
            if(answer[j] === before){
                count++;
            } else{
                string += `${count}${before}`;
                count = 1;
                before = answer[j];
            }
        }
        
        answer = `${string}${count}${before}`;
    }
    
    return answer;
};