输入数字n然后输出0到n的全排列

输入：2
输出：012 021 102 120 201 210

private static Set<String> result = new HashSet<String>();

public static void allSort(int number) {
    if (number < 0) {
        return;
    }
    String str="";
    for (int i = 0;i <= number; i++) {
        // 拼串
        str+=i;
    }
    char[] ch = str.toCharArray();
    allSort(ch,0,str.length());
}
public static void allSort(char[] str,int start,int end) {
    if (str == null || start > end || start < 0)
        return;
    if (start == end)
        // 去重
        result.add(String.valueOf(str));

    for (int i = start; i < end; i++) {
        swap(str,i,start);
        allSort(str,start + 1,end);
        // 还原
        swap(str,i,start);
    }
}

public static void swap(char[] str,int left,int right) {
    char temp = str[left];
    str[left] = str[right];
    str[right] = temp;
}