LeetCode 400 Nth Digit

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本文介绍了一种高效算法来找到无限整数序列（1,2,3,4...）中的第N位数字。该算法通过逐步缩小搜索范围，能够快速定位目标数字，并返回所需的位值。

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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 int findNthDigit(int n) {
		long i = 9;
		int count = 1;
		int pre = 1;
		while (n >i*(count)) {
			n-=i*(count++);
			i *= 10;
			pre *= 10;
		}
		int num =  (n-1) /count+pre;
		char c = String.valueOf(num).charAt((n-1)%count);
		return Character.getNumericValue(c);
	}