剑指offer 17. 打印从1到最大的n位数

题目描述

解题思路

class Solution {
    
    
    public int[] res;
    public int indexOfRes = 0;

    public int[] printNumbers(int n) {
    
    
        res = new int[(int)Math.pow(10, n) - 1];
        //保存每一个全排列
        char[] num = new char[n];
        backtrack(num, 0);
        return res;
    }

    //n位数字的全排列，每一位都有 '0'~'9' 十种选择
    public void backtrack(char[] num, int indexOfNum) {
    
    
        if (indexOfNum == num.length) {
    
    
            save(num);
            return;
        }
        for (char i = '0'; i <= '9'; i++) {
    
    
            num[indexOfNum] = i;
            backtrack(num, indexOfNum + 1);
        }
    }
    //将 num 数组表示的数字去除掉高位多余的'0'后存到 res[indexOfRes]中
    public void save(char[] num) {
    
    
        boolean isBegin0 = true;
        String stringOfNum = "";   //保存最终数字的 string 形式

        for (int i = 0; i < num.length; i++) {
    
    
            if (isBegin0 && (num[i] != '0'))
                isBegin0 = false;

            if (!isBegin0) {
    
    
                stringOfNum += num[i];
            }
        }
        //注意，要剔除全为0的情况
        if (!isBegin0) {
    
    
            res[indexOfRes++] = Integer.valueOf(stringOfNum);
        }
    }
}