題目描述：一個(gè)鏈表，奇數(shù)位升序偶數(shù)位降序，讓鏈表變成升序的。

比如：1 8 3 6 5 4 7 2 9，最后輸出1 2 3 4 5 6 7 8 9。

分析：

這道題可以分成三步：

首先根據(jù)奇數(shù)位和偶數(shù)位拆分成兩個(gè)鏈表。

然后對偶數(shù)鏈表進(jìn)行反轉(zhuǎn)。

最后將兩個(gè)有序鏈表進(jìn)行合并。

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package com.xxx;/*/ 一個(gè)鏈表，奇數(shù)位升序偶數(shù)位降序，讓鏈表變成升序的。比如：1 8 3 6 5 4 7 2 9，最后輸出1 2 3 4 5 6 7 8 9*/ /*** create by ziqiiii*/ public class Test {public static class Node {int val;Node next;Node(int x) { val = x; }}public static void main(String[] args){Node head = init();System.out.println("original:");printNode(head);Node[] nodes = getList(head);Node node1 = nodes[0];Node node2 = nodes[1];System.out.println("node1:");printNode(node1);System.out.println("node2:");printNode(node2);node2 = reverse(node2);System.out.println("reverse node2:");printNode(node2);Node result = mergeNode(node1,node2);System.out.println("result:");printNode(result);}public static void printNode(Node head){System.out.print(head.val);head=head.next;while(head!=null){System.out.print("->"+head.val);head=head.next;}System.out.println();}public static Node init(){Node node1 = new Node(1);Node node2 = new Node(8);Node node3 = new Node(3);Node node4 = new Node(6);Node node5 = new Node(5);Node node6 = new Node(4);Node node7 = new Node(7);Node node8 = new Node(2);Node node9 = new Node(9);node1.next = node2;node2.next = node3;node3.next = node4;node4.next = node5;node5.next = node6;node6.next = node7;node7.next = node8;node8.next = node9;return node1;}public static Node[] getList(Node head){Node head1=null;Node head2=null;Node cur1 = null;Node cur2 = null;int count=1;while(head != null){if(count % 2 ==1){ //奇數(shù)位, 升序if(cur1==null){head1=head;cur1=head1;}else{cur1.next=head;cur1=head;}}else{ //偶數(shù)位, 降序if(cur2==null){head2=head;cur2=head2;}else{cur2.next=head;cur2=head;}}head=head.next;count++;}cur1.next=null;//一定要給兩個(gè)新的鏈表結(jié)尾nullcur2.next=null;Node[] nodes = new Node[]{head1,head2};return nodes;}public static Node reverse(Node head){Node pre = null;Node next = null;while(head != null){next = head.next;head.next=pre;pre=head;head=next;}return pre;}public static Node mergeNode(Node node1,Node node2){if(node1==null){return node2;}if(node2==null){return node1;}Node head = null;Node cur = null;if(node1.val<=node2.val){head=node1;node1=node1.next;head.next=null;cur = head;}else{head=node2;node2=node2.next;head.next=null;cur = head;}while(node1!=null && node2!=null){if(node1.val<=node2.val){cur.next=node1;node1=node1.next;cur=cur.next;cur.next=null;}else{cur.next=node2;node2=node2.next;cur=cur.next;cur.next=null;}}if(node1 !=null){cur.next=node1;}if(node2 !=null){cur.next=node2;}return head;} }

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參考自：[算法]頭條面試—奇數(shù)位升序偶數(shù)位降序鏈表排序

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