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.
Input: l1 = [1,2,4], l2 = [1,3,4]
Output: [1,1,2,3,4,4]
Input: l1 = [], l2 = []
Output: []
Input: l1 = [], l2 = [0]
Output: [0]
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} l1
* @param {ListNode} l2
* @return {ListNode}
*/
var mergeTwoLists = function(l1, l2) {
let tmp = new ListNode();
let tmpHead = tmp;
tmp.next = new ListNode();
tmp = tmp.next;
// handle corner cases including they are empty
if (l1 === null && l2 === null) {
return l1;
} else if (l1 === null) {
return l2;
} else if (l2 === null) {
return l1;
}
// handle when both l1 and l2 are not empty
while ( l1 && l2) {
if ( l1.val <= l2.val) {
tmp.val = l1.val;
l1 = l1.next;
} else {
tmp.val = l2.val;
l2 = l2.next;
}
tmp.next = new ListNode();
tmp = tmp.next;
}
// handle rest part of l1 after handling completely both of l1 and l2
while (l1 != null) {
tmp.val = l1.val;
tmp.next = l1.next;
tmp = tmp.next;
l1 = l1.next;
}
// handle rest part of l2 after handling completely both l1 and l2
while (l2 != null) {
tmp.val = l2.val;
tmp.next = l2.next;
tmp = tmp.next;
l2 = l2.next;
}
// return merged result
return tmpHead.next;
};