reorder-list

reorder-list

描述

Given a singly linked list L: L 0→L 1→…→L n-1→L n,
reorder it to: L 0→L n →L 1→L n-1→L 2→L n-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}.

代码

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public void reorderList(ListNode head) {
        if(head==null){
            return;
        }
        ListNode[] points=new ListNode[20000];
        int i=0;
        for(ListNode node=head;node!=null;node=node.next,i++){
            points[i]=node;
        }
        int n=i;
        for(i=0;i<n/2;i++){
            points[i].next=points[n-i-1];
            points[n-i-1].next=points[i+1];
            if(i+1==(n/2)){
                if(points[i+1].next!=null){
                    points[i+1].next=null;
                }
            }
        }
    }
}