劍指Offer-14-打印從1到最大的n位數

import java.util.Arrays;

/**
 * 打印從1到最大的n位數 : https://leetcode-cn.com/problems/da-yin-cong-1dao-zui-da-de-nwei-shu-lcof/
 * @Description
 */
public class Test15 {
    public int[] printNumbers(int n) {
        int end = (int) Math.pow(10,n) - 1;
        int[] res = new int[end];
        for (int i = 0; i < end ; i++) {
            res[i] = i + 1;
        }
        return res;
    }

    //考慮大數問題
    private int[] res;
    private int nine = 0, count = 0, start, n;
    private char[] num, loop = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
    public int[] printNumbers2(int n) {
        this.n = n;
        res = new int[(int)Math.pow(10, n) - 1];
        num = new char[n];
        start = n - 1;
        dfs(0);
        return res;
    }
    private void dfs(int x) {
        if(x == n) {
            String s = String.valueOf(num).substring(start);
            if(!s.equals("0")) res[count++] = Integer.parseInt(s);
            if(n - start == nine) start--;
            return;
        }
        for(char i : loop) {
            if(i == '9') nine++;
            num[x] = i;
            dfs(x + 1);
        }
        nine--;
    }
    public static void main(String[] args) {
        System.out.println(Arrays.toString(new Test15().printNumbers(6)));
    }
}