Java菜鸟的面试准备（一）

来源：互联网发布：平板看电视直播软件编辑：程序博客网时间：2024/05/18 01:37

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

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