【LeetCode】剑指 Offer 44. 数字序列中某一位的数字

• 【LeetCode】剑指 Offer 44. 数字序列中某一位的数字

package offer;

public class Solution44 {
    public static void main(String[] args) {
        int n = 11;
        Solution44 solution = new Solution44();
        System.out.println(solution.method(n));
    }

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

//时间复杂度为 O(logn)
//空间复杂度为 O(logn)