java 单链表list 转置（反转） 普通与递归

单链表的转置 （反转）  

普通方法  通过循环与临时变量来转置   优点是节省内存开销

public void commonReverse(){
    	Node curr = head;
    	Node reve = null;
    	while(curr != null){
    		Node temp = curr;
    		curr = curr.next;
    		temp.next = reve;
    		reve = temp;
    	}
    	
    }

解析：当list = a1 a2 a3 a4 时

运算方式

第一轮：curr = a1 ; temp = a1 ; curr = a2 ; a1.next = null ; reve = a1;

第二轮：curr = a2 ; temp = a2 ; curr = a3 ; a2.next = a1 ; reve = a2;

第三轮：curr = a3 ; temp = a3 ; curr = a4 ; a3.next = a2 ; reve = a3;

第四轮：curr = a4 ; temp = a4 ; curr = null; a4.next = a3;reve = a4;

消耗内存最小 也容易理解

递归算法

 public Node recursionReverse(Node head){
    	
    	if(head == null || head.next == null){
    		return head;
    	}
    	
    	Node tail = recursionReverse(head);
    	head.next.next = head;
    	head.next = null;
    	
    	return tail;
    	
    } 

解析：当list = a1 a2 a3 a4 时

运算方式

第一轮 ： head = a1; head.next.next = head; head.next =null; 两个方法压入栈中 其中head = a1;

第二轮 ： head = a2; head.next.next = head;head.next =null; 两个方法压入栈中 其中head = a2;

第三轮 ： head = a3; head.next.next = head;head.next =null; 两个方法压入栈中 其中head = a3;

第四轮 ： head = a4; 返回方法栈 取出第三轮剩余方法执行

第三轮剩余方法：head = a3 ; a3.next = a4 ; a4.next = a3; a3.next = null;

第二轮剩余方法：head = a2 ; a2.next = a3 ; a3.next = a2; a2.next = null;

第一轮剩余方法：head = a1 ; a1.next = a2 ; a2.next = a1; a1.next = null;

完毕