reorder-list(Leetcode)

题目描述

Given a singly linked list L: L0→L1→…→Ln-1→Ln,

reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…

You must do this in-place without altering the nodes’ values.

For example,

Given{1,2,3,4}, reorder it to{1,4,2,3}.

根据提议，可以将问题分解为一下几个步骤解决。

找到链表的中间结点

将链表的后半部分反转（中间结点之后的部分）

将链表的前半部分和后半部分进行重排

package sxd.learn.java.leetcode;

/**
*
* @author lab
* 2016/5/30
* linked-list-cycle-ii
* Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
*/
public class Leetcode9 {

public static void main(String[] args) {
// TODO Auto-generated method stub
ListNode node1 = new ListNode(1);
ListNode node2 = new ListNode(2);
ListNode node3 = new ListNode(3);
ListNode node4 = new ListNode(4);
ListNode node5 = new ListNode(5);
ListNode node6 = new ListNode(6);

node1.next = node2;
node2.next = node3;
node3.next = node4;
node4.next = node5;
node5.next = node6;
node6.next = node3;

System.out.println(detectCycle(node1).val);
}

public static ListNode detectCycle(ListNode head) {
if(head == null)
return null;
ListNode fast = head;
ListNode slow = head;

boolean isCycle = false;

while(fast.next != null && fast.next.next != null){
fast = fast.next.next;
slow = slow.next;
if(slow.equals(fast)){
isCycle = true;
break;
}
}

if(isCycle){
fast = head;
while(!fast.equals(slow)){
fast = fast.next;
slow = slow.next;
}
return fast;
}else{
return null;
}

}
}