400. Nth Digit

原题

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:

Input:3Output:3

Example 2:

Input:11Output: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.

代码实现

//for this issue, there are two different ways to decribe a number        //1 element. this is our common way        //2 Nth digit. this is a new way        public int FindNthDigit(int n)        {            long bas = 9;            int digits = 1, i = 0;            //first: getting n which digit is in            // prevent overflowing.             //Since bas is long, so result of bas*digits is auto imporved as long            while (n > bas * digits)             {                n -= (int)(bas * (digits++)); //nth                i += (int)bas; //number of pasted elements                bas *= 10; //1 digit->9; 2 digits->90; 3 digits->900, ...               }            //second: Nth digit ->element            //in all numbers containing digits, pasted numbers            int pasted = (int)((n - 1) / digits);            int element = pasted + i + 1;            //third: once getting the element Nth digits stands,            //(n-1)%digits of element is solution            int nth = (n - 1) % digits;            return element.ToString()[nth] - '0';        }

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