400. Nth Digit - Jing blog -

Find the n^th 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.

思路：

这道题其实停费脑子的，先要找到区间，然后找到位置

class Solution {
    public int findNthDigit(int n) {
        if(n<10) return n;
        long num = 9;
        int count = 1;
        while(n > count * num){
            n -= num * count;
            count ++;
            num *= 10;
        }
        long res = num/9 + (n-1)/count;
        return Integer.parseInt(String.valueOf(res).substring((n-1)%count, (n-1)%count+1));
    }
}

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