[数据结构与算法]1.4.1 链表简单

链表反转
https://leetcode-cn.com/problems/reverse-linked-list/

    public ListNode reverseList(ListNode head) {
        if(head ==null || head.next ==null){
            return head;
        }
        ListNode next, cur, pre;
        pre = head;
        cur = head.next;
        head.next = null;
        while(cur!=null){
            next = cur.next;
            cur.next =  pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }

链表是否有环
https://leetcode-cn.com/problems/linked-list-cycle/
这个也是经典题目，解法比较巧妙。

    public boolean hasCycle(ListNode head) {
        if(head==null)
            return false;
        ListNode fast = head, slow = head;
        while(true) {
            if(fast.next == null || fast.next.next == null)
                return false;
            fast = fast.next.next;
            slow = slow.next;
            if(fast == slow) {
                return true;
            }
        }
    }