題目描述：一個鏈表，特點是奇數(shù)位升序偶數(shù)位降序，使得鏈表變成升序的。

• 分析
• 代碼
• • 節(jié)點類:
  • main方法:
  • 初始化方法：
  • 按照奇偶位拆分成兩個鏈表:
  • 反轉(zhuǎn)鏈表:
  • 合并兩個有序鏈表(非遞歸)：
  • 合并兩個有序鏈表(遞歸)：

分析

這道題可以分成三步：
首先根據(jù)奇數(shù)位和偶數(shù)位拆分成兩個鏈表。
然后對偶數(shù)鏈表進行反轉(zhuǎn)。
最后將兩個有序鏈表進行合并（合并兩種實現(xiàn)方式一種是遞歸另外一種是非遞歸）。

代碼

節(jié)點類:

class Node {int value;Node next;Node(int x) {value = x;next = null;} }

main方法:

public static void main(String[] args) {Node head = init();Node[] lists = getLists(head);Node head1 = lists[0];Node head2 = lists[1];head2 = reverseList(head2);// head = CombineList(head1, head2);head = mergeTwoLists(head1, head2);while(head != null) {System.out.println(head.value);head = head.next;} }

初始化方法：

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; }

按照奇偶位拆分成兩個鏈表:

public static Node[] getLists(Node head) {Node head1 = null;Node head2 = null;Node cur1 = null;Node cur2 = null;int count = 1;while(head != null) {if(count%2 == 1) {if(head1 == null) {cur1 = head;head1 = cur1;} else {cur1.next = head;cur1 = cur1.next;}} else {if(head2 == null) {cur2 = head;head2 = cur2;} else {cur2.next = head;cur2 = cur2.next;}}count++;head = head.next;}cur1.next = null;cur2.next = null;Node[] list = new Node[]{head1,head2};return list; }

反轉(zhuǎn)鏈表:

public static Node reverseList(Node head) { Node pre = null;Node next = null;while(head !=null) {next = head.next;head.next = pre;pre = head;head = next;}return pre; }

合并兩個有序鏈表(非遞歸)：

public static Node CombineList(Node head1, Node head2) {if(head1 == null || head2 == null) {return head1 != null ? head1 : head2;} Node head = head1.value < head2.value ? head1 : head2;Node cur1 = head == head1 ? head1 : head2;Node cur2 = head == head1 ? head2 : head1;Node pre = null;Node next = null;while(cur1 != null && cur2 != null) {if(cur1.value < cur2.value) {pre = cur1;cur1 = cur1.next;} else {next = cur2.next;pre.next = cur2;cur2.next = cur1;pre = cur2;cur2 = next;}}pre.next = cur1 == null ? cur2 : cur1;return head; }

合并兩個有序鏈表(遞歸)：

public static Node mergeTwoLists(Node l1, Node l2) {if(l1 == null || l2 == null){return l1 != null ? l1 : l2;}Node head = null;if(l1.value > l2.value){head = l2;head.next = mergeTwoLists(l1,l2.next);} else {head = l1;head.next = mergeTwoLists(l1.next,l2);}return head; }

總結(jié)

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