[LeetCode] 400. Nth Digit
Find the nth digit of the infinite integer sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...
Note:
n is positive and will fit within the range of a 32-bit signed integer (n < 231).
n is positive and will fit within the range of a 32-bit signed integer (n < 231).
Example 1:
Input: 3 Output: 3
Example 2:
Input: 11 Output: 0 Explanation: The 11th digit of the sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ... is a 0, which is part of the number 10.
用暴力搜索 會超時, 所以這是純數學題 數字是有規律的 我們把它分成9個 domain. 每個domain 代表 一位數, 兩位數, 三位數...
#1 1-9
#2 10-99
#3 100-999
#4 1000-9999
#5 10000-99999
#6 100000-999999
#7 1000000-9999999
#8 10000000-99999999
#9 100000000-99999999
這樣就好做了,思路是
1. 先找出 n 是在哪個 domain
2. 再找出 是domain 裡哪一個數, 假設是 whn
3. 最後找出 whn 裡 相對應的 digit
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