_400.java

package com.fishercoder.solutions;

/**
 * 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).

 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.
 */
public class _400 {

    public static class Solution1 {
        /**
         * credit: https://discuss.leetcode.com/topic/59314/java-solution:
         *
         * 1. find the length of the number where the nth digit is from 2. find the actual number where
         * the nth digit is from 3. find the nth digit and return
         */
        public int findNthDigit(int n) {
            int len = 1;
            long count = 9;
            int start = 1;

            while (n > len * count) {
                n -= len * count;
                len += 1;
                count *= 10;
                start *= 10;
            }

            start += (n - 1) / len;
            String s = Integer.toString(start);
            return Character.getNumericValue(s.charAt((n - 1) % len));
        }
    }
}