单链表

class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
    }
}
public class LeetCode206 {

    public ListNode reverseList(ListNode head) {
        // 翻转列表，关键点是要知道当前列表和前一个列表
        ListNode cur = head , prev = null;
        // 遍历一遍
        while(cur != null){
            //prev ->cur ->cur.next  
            ListNode next = cur.next;
            cur.next = prev;
            prev = cur;
            cur = next;
        }
        return prev;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // 单链表
        ListNode head = new ListNode();
        ListNode node1 = new ListNode();
        ListNode node2 = new ListNode();
        ListNode node3 = new ListNode();
        ListNode node4 = new ListNode();
        head.next = node1;
        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = null;
        ListNode node = new LeetCode206().reverseList(head);
        while(node != null){
            System.out.print(node.val +" ");
            node = node.next;
        }
    }
}