21. Merge Two Sorted Lists

🟩 Easy

Solution

My Solution - using pointers

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
    head := &ListNode{}
    curr := head

    for list1 != nil && list2 != nil {
        if list1.Val < list2.Val {
            curr.Next = list1
            list1 = list1.Next
        } else {
            curr.Next = list2
            list2 = list2.Next
        }

        curr = curr.Next
    }

    if list1 == nil {
        curr.Next = list2
    } else if list2 == nil{
        curr.Next = list1
    }

    return head.Next
}

result

My solution-2 - using recursion

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
    if list1 == nil{
        return list2
    }

    if list2 == nil {
        return list1
    }

    if list1.Val < list2.Val {
        list1.Next = mergeTwoLists(list1.Next, list2)
        return list1
    } else {
        list2.Next = mergeTwoLists(list2.Next, list1)
        return list2
    }
}

result

Leetcode: link