Merge Two Sorted Lists 解答

Question

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.

Solution

The key to the solution here is to create a new linked list by creating a fake head.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l2 == null)
            return l1;
        if (l1 == null)
            return l2;
        ListNode fakeHead = new ListNode(0);
        ListNode tmp = fakeHead;
        ListNode p1 = l1, p2 = l2;
        while (p1 != null && p2 != null) {
            if (p1.val < p2.val) {
                tmp.next = p1;
                p1 = p1.next;
            } else {
                tmp.next = p2;
                p2 = p2.next;
                
            }
            tmp = tmp.next;
        }
        while (p1 != null) {
            tmp.next = p1;
            tmp = tmp.next;
            p1 = p1.next;
        }
        while (p2 != null) {
            tmp.next = p2;
            tmp = tmp.next;
            p2 = p2.next;
        }
        return fakeHead.next;
    }
}