Leetcode-Reorder List

作者：disappearedgod

文章出处：http://blog.csdn.net/disappearedgod/article/details/24019729

时间：2014-8-20

题目

Reorder List

 Total Accepted: 9237 Total Submissions: 47615My Submissions

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}.

 Definition for singly-linked list. public class ListNode {     int val;     ListNode next;     ListNode(int x) {         val = x;         next = null;     } }

/** * 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 || head.next == null)            return;        ListNode p = head;        ListNode reversal = new ListNode(head.val);        ListNode rp = new ListNode(head.val);//这里为了形成一个环 所以先new一个点，而不是null，在for里面形成这个点        ListNode tmp = null;        int length = 0;        for(p = head.next; p !=null; p = p.next){            tmp = new ListNode(p.val);            tmp.next = rp;            rp = tmp;//这两句形成环 如果p = head 的情况下            length++;        }        reversal = rp;        //printList(reversal);        p = head;        rp = reversal;        head = rp;        ListNode t_pN = null;        ListNode t_rpN = null;        for(int i = 0; i < length/2; i++){            t_pN = p.next;            t_rpN = rp.next;            p.next = rp;            rp.next = t_pN;            p = t_pN;            rp = t_rpN;        }        if(p != null)            if(length%2!=0 && p.next !=null)                p.next.next = null;            else                p.next = null;    }}

调试文件

package List;/** * Created by yuyan on 14-8-20. */public class ReorderList extends ListTest {    @Override    protected void work(ListNode head) {        super.work(head);        if(head == null || head.next == null)            return;        ListNode p = head;        ListNode reversal = new ListNode(head.val);        ListNode rp = new ListNode(head.val);        ListNode tmp = null;        int length = 0;        for(p = head.next; p !=null; p = p.next){            tmp = new ListNode(p.val);            tmp.next = rp;            rp = tmp;            length++;        }        reversal = rp;        p = head;        rp = reversal;        ListNode t_pN = null;        ListNode t_rpN = null;        for(int i = 0; i < length/2; i++){            t_pN = p.next;            t_rpN = rp.next;            p.next = rp;            rp.next = t_pN;            p = t_pN;            rp = t_rpN;        }        if(p != null)            if(length%2!=0 && p.next !=null)                p.next.next = null;            else                p.next = null;    }    public static void main(String[] args){        ReorderList test = new ReorderList();        int[] a = {1,2,3};        ListNode head = test.buildTestListFromArray(a);        //test.printList(head);        test.work(head);        test.printList(head);    }}

package List;/** * Created by yuyan on 14-8-20. */public class ListTest {    protected void work(ListNode head){    }    protected void printList(ListNode head){        if(head == null){            System.out.print("[ ]");            return;        }        for(; head.next !=null; head = head.next){            System.out.print("["+ head.val+"]->");        }        System.out.print("["+ head.val+"]");    }    protected ListNode buildTestListFromArray(int[] a){        ListNode testList = new ListNode(a[0]);        ListNode p = testList;        for(int i = 1 ; i < a.length; i++){            ListNode tmp = new ListNode(a[i]);            p.next = tmp;            p = p.next;        }        return testList;    }    protected ListNode buildDescendTestList(int N){        ListNode testList = null;        for(int i = 0 ; i < N; i++){            ListNode tmp = new ListNode(i+1);            tmp.next = testList;            testList = tmp;        }        return testList;    }    protected ListNode buildAscendTestList(int N){        ListNode testList = new ListNode(1);        ListNode p = testList;        for(int i = 1 ; i < N; i++){            ListNode tmp = new ListNode(i+1);            p.next = tmp;            p = p.next;        }        return testList;    }    public static void main(String[] args){        ListTest t = new ListTest();        ListNode testList = t.buildAscendTestList(10);        t.printList(testList);    }}

返回

LeetCode Solution(持续更新，java>c++)