蓝桥杯（3.1）

92. 递归实现指数型枚举

import java.util.Scanner;

public class Main {
	static int N = 16;
	static int n;
	static int[] st = new int[N];	

	public static void dfs(int u) {
		if(u > n) {
			for(int i=1;i<=n;i++) {
				if(st[i] == 1)
					System.out.print(i+" ");
			}
			System.out.println();
			return ;
		}
		
		st[u] = 2;
		dfs(u+1);
		st[u] = 0;		
		
		st[u] = 1;
		dfs(u+1);
		st[u] = 0;		
	}
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		dfs(1);
	}
}

94. 递归实现排列型枚举

import java.util.Scanner;

public class Main {
	static int N = 10;
	static int n;
	static int[] st = new int[N];	
	static boolean[] vis = new boolean[N];	

	public static void dfs(int u) {
		if(u > n) {
			for(int i=1;i<=n;i++) {
					System.out.print(st[i]+" ");
			}
			System.out.println();
			return ;
		}
		for(int i=1;i<=n;i++) {
			if(!vis[i]) {
				st[u] = i;
				vis[i] = true;
				dfs(u+1);
				st[u] = 0;
				vis[i] = false;
			}
		}
		
	}
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		dfs(1);
	}
}

93. 递归实现组合型枚举

import java.util.Scanner;

public class Main {
	static int N = 26;
	static int n;
	static int m;
	static int[] st = new int[N];	

	public static void dfs(int u,int start) {
		if(u > m) {
				for(int i=1;i<=m;i++) {
					System.out.print(st[i]+" ");
				}
				System.out.println();
				return ;
		}
		for(int i=start;i<=n;i++) {
				st[u] = i;
				dfs(u+1,i+1);
				st[u] = 0;
			}		
	}
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		m = sc.nextInt();
		//u和start
		dfs(1,1);
	}
}