LeetCode 0400 - Nth Digit

Desicription

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).

Example 1:

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Input:
3

Output:
3

Example 2:

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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.

Solution

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class Solution {
public:
int findNthDigit(int n) {
long long start = 1;
long long len = 1;
long long count = 9;
while(n > len * count) {
n -= len * count;
len++;
count *= 10;
start *= 10;
}
return std::to_string(start + (n - 1) / len)[(n - 1) % len] - '0';
}
};