出處： https://leetcode.com/explore/interview/card/top-interview-questions-easy/127/strings/886/
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 fromcountAndSay(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
/**
* @param {number} n
* @return {string}
*/
var countAndSay = function(n) {
if (n === 1) return '1'
const theLoop = (num) => {
let current = num[0]
let count = 0
let str = ''
let i = 0
while(i < num.length) {
if (current === num[i]) {
count++
} else {
str += count + current
current = num[i]
count = 1
}
i++
}
str += count + current
return str
}
let res = "1"
for(let i = 1; i < n; i++) {
res = theLoop(res)
}
return res
};思路
又是一個遞迴的 loop， 從 n 等於 2 開始進入迴圈。
逐一偵測每一個字是否和上一個字相同，若相同則累加數字，不同則進行結算。
