LeetCode 1556. Thousand Separator

題目:

在數字千位位置加一個string的點。

Example 1:

Input: n = 987
Output: "987"

Example 2:

Input: n = 1234
Output: "1.234"

Example 3:

Input: n = 123456789
Output: "123.456.789"

Example 4:

Input: n = 0
Output: "0"

思路:

1. 因為是return 一個string format，因此initial
   result = " "
2. input的integer先轉換成string format
   n = str(n)
3. count =0 每數三個加一個點
4. 讀string由右往左讀，因此最後一位的index 是len(n)-1
   for i in range(len(n)-1,-1,-1):
5. if count < 3:
   result = n[i] +result 注意這邊的位置 n[i]先
   count +=1
6. if count ==3 and i ≥1:
   result = “.” +result
   count = 0
7. return result

Coding:

class Solution:
    def thousandSeparator(self, n: int) -> str:
        result =''
        n = str(n)
        count = 0
        
        for i in range(len(n)-1, -1,-1):       
            if count < 3:
                result = n[i] + result
                count += 1
            if count == 3 and i >= 1:
                result = '.' + result
                count = 0
        return result