singularity

21. Merge Two Sorted Linked Lists

O(n)


var mergeTwoLists = function(list1, list2) {

    let newHead = dummyHead = new ListNode(); 

    while(list1 && list2){
        if (list1.val < list2.val){
            dummyHead.next = list1;
            list1 = list1.next;
        } else {
            dummyHead.next = list2;
            list2 = list2.next;
        }
        dummyHead = dummyHead.next;
    }  

    if(list1){
        dummyHead.next = list1;
    }

    if(list2){
        dummyHead.next = list2;
    }    

    return newHead.next;
};



# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

class Solution:
    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        newHead = dummyHead = ListNode()
        
        while list1 and list2:
            if list1.val < list2.val:
                dummyHead.next = list1
                list1 = list1.next
            else:
                dummyHead.next = list2
                list2 = list2.next
            dummyHead = dummyHead.next
        
        dummyHead.next = list1 if list1 else list2 

        return newHead.next