Merge Two Sorted Lists

Easy LinkedIn Linked List

LintCode: http://www.lintcode.com/en/problem/merge-two-sorted-lists/

LeetCode: https://leetcode.com/problems/merge-two-sorted-lists/#/description

Question

Merge two sorted (ascending) linked lists and return it as a new sorted list. The new sorted list should be made by splicing together the nodes of the two lists and sorted in ascending order.

Example
Given 1->3->8->11->15->null, 2->null , return 1->2->3->8->11->15->null .

Thinking

• One while loop to build a new list
• Some people consider about recursion, but I think the while loop is very straightforward.

Solution

Java

/**
 * 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 (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        ListNode merged = new ListNode(0);
        ListNode tmp = merged;
        while (l1 != null && l2!= null) {
            if (l1.val < l2.val) {
                tmp.next = l1;
                l1 = l1.next;
            } else {
                tmp.next = l2;
                l2 = l2.next;
            }
            tmp = tmp.next;
        }
        if (l1 != null) {
            tmp.next = l1;
        } else {
            tmp.next = l2;
        }
        return merged.next;
    }
}