Java菜鸟的面试准备（一）

最近各种互联网公司内推、校招接踵而至，作为一名JAVA开发小菜鸟，使出了洪荒之力还有一种HOLD不住的赶脚，所以想在这里理理思路，闲话少说。
今天从链表开始

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

问题一：翻转链表
迭代：

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

    }
}

递归：

public ListNode reverseList2(ListNode head){
        if (head==null||head.next==null) {
            return head;
        }
        ListNode cur = head.next;
        ListNode newHead = reverseList2(cur);

        head.next=null;
        cur.next=head;

        return newHead;

    }

问题二：判断链表是否有环

public class LinkedListCycle {
    public boolean hasCycle(ListNode head) {
        if (head==null||head.next==null) {
            return false;
        }
        ListNode fast=head;
        ListNode slow =head;
        //fast==null fast==slow
        while (fast.next!=null&&fast.next.next!=null) {
            fast=fast.next.next;
            slow=slow.next;
            if (fast==slow) {
                return true;
            }
        }
        return false;

    }

     public ListNode detectCycle(ListNode head) {
         if (head==null||head.next==null) {
                return null;
            }
            ListNode fast=head;
            ListNode slow =head;
            //fast==null fast==slow
            while (fast.next!=null&&fast.next.next!=null) {
                fast=fast.next.next;
                slow=slow.next;
                if (fast==slow) {
                    fast=head;
                    while (fast!=slow) {
                        fast=fast.next;
                        slow=slow.next;

                    }
                    return fast;
//                  return true;
                }
            }
            return null;


        }

}

待续