递归实现指数型枚举

import java.util.*;

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

递归实现组合型枚举

import java.util.*;

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

递归实现排列型枚举

import java.util.*;

public class Main {
    public static void dfs(int u, int n, int[] path, boolean[] st) {
        if (u > n) {
            for (int i = 1; i <= n; i++) System.out.print(path[i] + " ");
            System.out.println();
        }
        for (int i = 1; i <= n; i++) {
            if (!st[i]) {
                path[u] = i;
                st[i] = true;
                dfs(u + 1, n, path, st);    
                st[i] = false;
            }
        }
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int[] path = new int[n + 1];
        boolean[] st = new boolean[n + 1];
        dfs(1, n, path, st);
        
    }
}