MergeTwoSortedLists.java

package leetcode;

/**
 * @author eko
 *
 * 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.
 *
 * Example:
 *
 * Input: 1->2->4, 1->3->4
 * Output: 1->1->2->3->4->4
 *
 */
public class MergeTwoSortedLists {
    public static void main(String[] args) {
        ListNode l1 = new ListNode(1);
        ListNode l2 = new ListNode(2);
        ListNode l3 = new ListNode(4);
        ListNode l4 = new ListNode(1);
        ListNode l5 = new ListNode(3);
        ListNode l6 = new ListNode(4);
        l1.next = l2;
        l2.next = l3;
        l4.next = l5;
        l5.next = l6;

        ListNode result = new MergeTwoSortedLists().mergeTwoLists(l1, l4);
        while (result!=null) {
            System.out.println(result.val);
            result = result.next;
        }
    }

    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) return l2;
        if (l2 == null) return l1;

        ListNode start;
        if (l1.val < l2.val) {
            start = l1;
            l1 = l1.next;
        } else {
            start = l2;
            l2 = l2.next;
        }

        ListNode index = start;

        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                index.next = l1;
                l1 = l1.next;
            } else {
                index.next = l2;
                l2 = l2.next;
            }
            index = index.next;
        }

        if (l1 != null) {
            index.next = l1;
        }

        if (l2 != null) {
            index.next = l2;
        }

        return start;
    }

    public static class ListNode {
        int val;
        ListNode next;

        ListNode(int x) {
            val = x;
        }
    }
}