LeetCode Top Interview 150

21. Merge Two Sorted Lists

Easy

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

Example 1:

Input: l1 = [1,2,4], l2 = [1,3,4]

Output: [1,1,2,3,4,4]

Example 2:

Input: l1 = [], l2 = []

Output: []

Example 3:

Input: l1 = [], l2 = [0]

Output: [0]

Constraints:

• The number of nodes in both lists is in the range [0, 50].
• -100 <= Node.val <= 100
• Both l1 and l2 are sorted in non-decreasing order.

Solution

type ListNode struct {
	Val  int
	Next *ListNode
}

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
	var sortedListNode, tail *ListNode = &ListNode{}, &ListNode{}
	// Start sortedListNode and tail node at the same position
	tail = sortedListNode
	for list1 != nil && list2 != nil {
		if list1.Val <= list2.Val {
			tail.Next = list1
			list1 = list1.Next
		} else {
			tail.Next = list2
			list2 = list2.Next
		}
		// Progress the tail further
		tail = tail.Next
	}
	if list1 != nil {
		tail.Next = list1
	}
	if list2 != nil {
		tail.Next = list2
	}
	return sortedListNode.Next
}

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