Nth Digit — LeetCode 400 Python Solution

The problem

Given an integer n, return the nth digit of the infinite integer sequence [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...].

Example

Input

n = 3

Output

3

Python solution

class Solution:
    def findNthDigit(self, n: int) -> int:
        k, cnt = 1, 9
        while k * cnt < n:
            n -= k * cnt
            k += 1
            cnt *= 10
        num = 10 ** (k - 1) + (n - 1) // k
        idx = (n - 1) % k
        return int(str(num)[idx])

Complexity

Pattern: Monotonic Stack

Answer "what is the next greater element" for every position in one pass. LeetCode 400. Nth Digit is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The monotonic stack guide has the Python template for the pattern and the 225 LeetCode problems that use it.

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