## Algorithm

Problem Name: 21. Merge Two Sorted Lists

You are given the heads of two sorted linked lists `list1` and `list2`.

Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.

Example 1:

```Input: list1 = [1,2,4], list2 = [1,3,4]
Output: [1,1,2,3,4,4]
```

Example 2:

```Input: list1 = [], list2 = []
Output: []
```

Example 3:

```Input: list1 = [], list2 = [0]
Output: [0]
```

Constraints:

• The number of nodes in both lists is in the range `[0, 50]`.
• `-100 <= Node.val <= 100`
• Both `list1` and `list2` are sorted in non-decreasing order.

## Code Examples

### #1 Code Example with C Programming

```Code - C Programming```

``````
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {

while (l1 && l2) {
if (l1->val  < = l2->val) {
p->next = l1;
l1 = l1->next;
} else {
p->next = l2;
l2 = l2->next;
}
p = p->next;
}

// chain remaining
if (l1) p->next = l1;
if (l2) p->next = l2;

return p;
}
``````
Copy The Code &

Input

cmd
list1 = [1,2,4], list2 = [1,3,4]

Output

cmd
[1,1,2,3,4,4]

### #2 Code Example with C++ Programming

```Code - C++ Programming```

``````
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if (!l1 || !l2) return l1 ? l1 : l2;
while (l1 && l2) {
if (l1->val  <  l2->val) {
cur->next = l1;
l1 = l1->next;
}
else {
cur->next = l2;
l2 = l2->next;
}
cur = cur->next;
}
cur->next = l1 ? l1 : l2;
}
};
``````
Copy The Code &

Input

cmd
list1 = [], list2 = []

Output

cmd
[]

### #3 Code Example with Java Programming

```Code - Java Programming```

``````
class Solution {
public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
if (list1 == null || list2 == null) {
return list1 == null ? list2 : list1;
}
ListNode prev = null;
while (list1 != null && list2 != null) {
if (list1.val  < = list2.val) {
prev = list1;
}
list1 = list1.next;
} else {
ListNode node = list2;
list2 = list2.next;
if (prev == null) {
node.next = list1;
prev = node;
} else {
prev.next = node;
node.next = list1;
prev = node;
}
}
}
if (list2 != null) {
prev.next = list2;
}
if (list1 != null) {
prev.next = list1;
}
}
}
``````
Copy The Code &

Input

cmd
list1 = [], list2 = [0]

Output

cmd
[0]

### #4 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const mergeTwoLists = function(l1, l2) {
if (l1 === null) return l2;
if (l2 === null) return l1;
if (l1.val  <  l2.val) {
l1.next = mergeTwoLists(l1.next, l2);
return l1;
} else {
l2.next = mergeTwoLists(l1, l2.next);
return l2;
}
};
``````
Copy The Code &

Input

cmd
list1 = [], list2 = [0]

Output

cmd
[0]

### #5 Code Example with Python Programming

```Code - Python Programming```

``````
class Solution:
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
if not l1: return l2
elif not l2: return l1
if l1.val < l2.val:
l1.next = self.mergeTwoLists(l1.next, l2)
return l1
else:
l2.next = self.mergeTwoLists(l1, l2.next)
return l2
``````
Copy The Code &

Input

cmd
list1 = [], list2 = []

Output

cmd
[]

### #6 Code Example with C# Programming

```Code - C# Programming```

``````
namespace LeetCode
{
public class _021_MergeTwoSortedLists
{
public ListNode MergeTwoLists(ListNode l1, ListNode l2)
{

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

current.next = l1 == null ? l2 : l1;
}
}
}

``````
Copy The Code &

Input

cmd
list1 = [1,2,4], list2 = [1,3,4]

Output

cmd
[1,1,2,3,4,4]