LeetCode Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

思路分析：这题是 LeetCode Sort List需要使用的merge两个有序链表使得结果仍然有序这个子过程，详细图解可以参见 LeetCode Sort List。时间复杂度O（m+n），空间复杂度O（1），是常量。与这题关系密切的题目还有Merge Sorted Array，Merge k Sorted Lists，Merge Intervals等，可以比较一下解法，熟练掌握。

AC Code

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { *         val = x; *         next = null; *     } * } */public class Solution {    public ListNode mergeTwoLists(ListNode head1, ListNode head2) {        ListNode fakeHead = new ListNode(0);        fakeHead.next = head1;        ListNode pre = fakeHead;        while(head1 != null && head2 != null){            if(head1.val < head2.val){                head1 = head1.next;            } else {                ListNode next = head2.next;                head2.next = pre.next;                pre.next = head2;                head2 = next;            }            pre = pre.next;        }        if(head2 != null){            pre.next = head2;        }        return fakeHead.next;    }}