Leecode brush questions record sword finger offer 44 A digit in a sequence of numbers

topic

The numbers are in 0123456789101112131415… Serializes the format of a string into a sequence of characters . In this sequence , The first 5 position （ From the subscript 0 Start counting ） yes 5, The first 13 Is it 1, The first 19 Is it 4, wait .

Please write a function , Ask for any n The number corresponding to bit .

Example 1：

Input ：n = 3
Output ：3
Example 2：

Input ：n = 11
Output ：0

Limit ：

0 <= n < 2^31

answer

class Solution {
    

    public int findNthDigit(int n) {
    
        int digit = 1;
        long start = 1;
        long count = 9;
        while (n > count) {
     // 1.
            n -= count;
            digit += 1;
            start *= 10;
            count = digit * start * 9;
        }
        long num = start + (n - 1) / digit; // 2.
        return Long.toString(num).charAt((n - 1) % digit) - '0'; 
    }
}