The idea of full arrangement in java

• The idea of ​​full arrangement, in fact, full arrangement is a kind of arrangement and combination, such as 1 2 3, so how many possible combinations are there?

  • According to our subjective consciousness, there are naturally six kinds of ①1 2 3 ②1 3 2 ③2 1 3 ④2 3 1 ⑤3 1 2 ⑥3 2 1

  • Next, explain the full arrangement idea in detail

  • package test;
    
    import java.util.*;
    
    public class Main {
    	
    	public static void main(String[] args) {
    		Scanner sc=new Scanner(System.in);
    		int n=sc.nextInt();  //输入n
    		int[] a=new int[n]; //创建数组a
    		for(int i=0;i<n;i++) {
    			a[i]=sc.nextInt(); // 获取数组a的元素
    		}
    		perm(a,0,n-1);
    	}
    	public static void perm(int[] a,int l,int r) { //l为左指针，r为右指针
    		if(l==r) System.out.println(Arrays.toString(a)); 
    		else {
    			for(int i=l;i<=r;i++) {
    				swap(a,i,l);  // 数组a[i]与a[l]作交换
    				perm(a,l+1,r); // 余下数组作全排列，固 左指针加1，即 l+1
    				swap(a,i,l); // 将数组还原防止重复
    			}
    		}
    	}
    	// 简单的作交换处理 ，定义 交换存储器 temp
    	public static void swap(int[] a,int i,int j) {
    		int temp = a[i];  
    		a[i]=a[j];
    		a[j]=temp;
    	}
    }
    

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