子集生成

输入：3
输出：1
          1 2 
          1 2 3
          2
          2 3
          3

位向量法：public class Main {

static int[] a;

public static void fun(int cur, int n) {
if (cur == n) {
for (int i = 0; i < cur; i++) {
if (a[i] == 1)
System.out.print(i + 1);
}
System.out.println();
return;
}
a[cur] = 1;// 选当前元素
fun(cur + 1, n);
a[cur] = 0;// 不选当前元素
fun(cur + 1, n);
}

public static void main(String[] args) {
Scanner in = new Scanner(System.in);
a = new int[100];
while (in.hasNext()) {
int n = in.nextInt();
fun(0, n);
}
}
}

增量构造法：
一次选出一个元素放到集合public class Main {

static int[] a;

public static void fun(int cur, int n) {
for (int i = 0; i < cur; i++) {
System.out.print(a[i] + " ");
}
if (cur != 0)
System.out.println();
int min = cur > 0 ? a[cur - 1] + 1 : 1;// 确定当前元素的最小可能值
for (int i = min; i <= n; i++) {
a[cur] = i;
fun(cur + 1, n);
}
}

public static void main(String[] args) {
Scanner in = new Scanner(System.in);
a = new int[100];
while (in.hasNext()) {
int n = in.nextInt();
fun(0, n);
}
}
}