合并两个排序的链表

题目描述

输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。

直接上代码：

package cn.yzx.nowcoder;


/** * 题目描述 * 输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。 * * @author yzx * */
public class MergeListNode {

    public static void main(String[] args) {
        ListNode head1 = new ListNode(1);
        ListNode testList = new ListNode(3);
        ListNode testList1 = new ListNode(5);
        head1.next = testList;
        testList.next = testList1;

        ListNode head2 = new ListNode(2);
        ListNode testList0 = new ListNode(4);
        ListNode testList01 = new ListNode(6);
        head2.next = testList0;
        testList0.next = testList01;

        ListNode res = MergeListNode.Merge1(head1, head2);
        while (res != null) {
            System.out.print(res.val + " ");
            res = res.next;
        }
    }

    public static class ListNode {
        int val;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }

    // 递归
    public static ListNode Merge(ListNode list1, ListNode list2) {
        if (list1 == null)
            return list2;
        else if (list2 == null)
            return list1;

        ListNode resNode = null;
        if (list1.val < list2.val) {
            resNode = list1;
            resNode.next = Merge(list1.next, list2);
        } else {
            resNode = list2;
            resNode.next = Merge(list1, list2.next);
        }
        return resNode;
    }

    // 非递归
    public static ListNode Merge1(ListNode list1, ListNode list2) {
        ListNode result = null;
        ListNode current = null;

        if (list1 == null)
            return list2;
        else if (list2 == null)
            return list1;

        while (list1 != null && list2 != null) {
            if (list1.val <= list2.val) {
                if (result == null) {
                    current = result = list1;
                } else {
                    current.next = list1;
                    current = current.next;
                }
                list1 = list1.next;
            } else {
                if (result == null) {
                    current = result = list2;
                } else {
                    current.next = list2;
                    current = current.next;
                }
                list2 = list2.next;
            }
        }
        if(list1 == null){
            current.next = list2;
        }
        if (list2 == null) {
            current.next = list1;
        }
        return result;
    }

    // 我突然脑袋短路的方法
    public static ListNode Merge2(ListNode list1, ListNode list2) {
        if (list1 == null)
            return list2;
        else if (list2 == null)
            return list1;
        else {
            ListNode resNode = null;
            if (list1.val <= list2.val) {
                resNode = list1;
                while (list1 != null || list2 != null) {
                    if (list1 == null) {
                        list1.next = list2;
                        return resNode;
                    } else if (list2 == null) {
                        return resNode;
                    } else {
                        if (list1.next != null) {
                            if (list1.val <= list2.val
                                    && list1.next.val > list2.val) {
                                ListNode tmp = list2;
                                list2 = list2.next;
                                tmp.next = list1.next;
                                list1.next = tmp;
                                list1 = tmp;
                            }
                            list1 = list1.next;
                        } else {
                            list1.next = list2;
                            return resNode;
                        }
                    }
                }
                return resNode;
            } else {
                resNode = list2;
                while (list2 != null || list1 != null) {
                    if (list2 == null) {
                        list2.next = list1;
                        return resNode;
                    } else if (list1 == null) {
                        return resNode;
                    } else {
                        if (list2.next != null) {
                            if (list2.val <= list1.val
                                    && list2.next.val > list1.val) {
                                ListNode tmp = list1;
                                list1 = list1.next;
                                tmp.next = list2.next;
                                list2.next = tmp;
                                list2 = tmp;
                            }
                            list2 = list2.next;
                        } else {
                            list2.next = list1;
                            return resNode;
                        }
                    }
                }
                return resNode;
            }
        }
    }
}