LeetCode_21. Merge Two Sorted Lists

21. Merge Two Sorted Lists

Easy

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

package leetcode.easy;

/**
 * Definition for singly-linked list. public class ListNode { int val; ListNode
 * next; ListNode(int x) { val = x; } }
 */
class ListNode {
	int val;
	ListNode next;

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

public class MergeTwoSortedLists {
	@org.junit.Test
	public void test() {
		ListNode l11 = new ListNode(1);
		ListNode l12 = new ListNode(2);
		ListNode l13 = new ListNode(4);
		l11.next = l12;
		l12.next = l13;
		l13.next = null;
		print(l11);

		ListNode l21 = new ListNode(1);
		ListNode l22 = new ListNode(3);
		ListNode l23 = new ListNode(4);
		l21.next = l22;
		l22.next = l23;
		print(l21);

		ListNode l = mergeTwoLists(l11, l21);
		print(l);
	}

	public static void print(ListNode l) {
		while (l != null) {
			System.out.print(l.val);
			if (l.next != null) {
				System.out.print("->");
			}
			l = l.next;
		}
		System.out.println();
	}

	public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
		ListNode head = new ListNode(0);
		ListNode p = head;

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

		if (l1 != null) {
			p.next = l1;
		}
		if (l2 != null) {
			p.next = l2;
		}

		return head.next;
	}
}