Add merge_two_linked_lists solution

neetcode/linked_list/merge_two_linked_lists/README.md

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+Merge Two Sorted Linked Lists
+You are given the heads of two sorted linked lists list1 and list2.
+
+Merge the two lists into one sorted linked list and return the head of the new sorted linked list.
+
+The new list should be made up of nodes from list1 and list2.
+
+Example 1:
+
+
+
+Input: list1 = [1,2,4], list2 = [1,3,5]
+
+Output: [1,1,2,3,4,5]
+Example 2:
+
+Input: list1 = [], list2 = [1,2]
+
+Output: [1,2]
+Example 3:
+
+Input: list1 = [], list2 = []
+
+Output: []
+Constraints:
+
+0 <= The length of the each list <= 100.
+-100 <= Node.val <= 100
+
+# Solution
+
+## Edge cases
+### Two empty
+l1 = []
+l2 = []
+
+r = None
+### l1 empty
+l1 = []
+l2 = [1,2,...,n]
+
+r = l2
+### l2 empty
+l1 = [1,2,...,n]
+l2 = []
+
+r = l1
+
+## Algorithm
+### 0
+      i     
+l1 = [1,2,4]
+
+      j     
+l2 = [1,3,5]
+
+r = []
+
+### 1
+Before: 
+
+      i     
+l1 = [1,2,4]
+
+      j     
+l2 = [1,3,5]
+
+r = []
+
+Step:
+```
+if i.val <= j.val:
+    r = i
+    i = i.next
+```
+
+After:
+
+        i   
+l1 = [1,2,4]
+
+      j     
+l2 = [1,3,5]
+
+r = [l10]
+
+### 2
+Before:
+        i   
+l1 = [1,2,4]
+
+      j     
+l2 = [1,3,5]
+
+r = [l10]
+
+Step:
+```
+if i.val <= j.val:
+    ---
+else:
+    r.next = j
+    j = j.next
+    r = r.next
+```
+After:
+        i   
+l1 = [1,2,4]
+
+        j  
+l2 = [1,3,5]
+
+r = [l10, l20]
+
+### 3
+Before:
+        i   
+l1 = [1,2,4]
+
+        j  
+l2 = [1,3,5]
+
+r = [l10, l20]
+
+Step:
+```
+if i.val <= j.val:
+    r.next = i
+    i = i.next
+    r = r.next
+else:
+    r.next = j
+    j = j.next
+    r = r.next
+```
+After:
+          j
+l1 = [1,2,4]
+
+        j  
+l2 = [1,3,5]
+
+r = [l10, l20, l11]

neetcode/linked_list/merge_two_linked_lists/main.py

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+from typing import Optional
+
+
+# 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]:
+        if not list1 and not list2:
+            return None
+        if not list1 and isinstance(list2, ListNode):
+            return list2
+        if not list2 and isinstance(list1, ListNode):
+            return list1
+        i = list1
+        j = list2
+        r = None
+        rf = None
+        while i or j:
+            print(f"i : {i.val if i else 'No value'}\nj : {j.val if j else 'No value'}\n")
+            if not j:
+                r.next = i
+                i = i.next
+                r = r.next
+                continue
+            if not i:
+                r.next = j
+                j = j.next
+                r = r.next
+                continue
+            if i.val <= j.val:
+                if not r:
+                    r = i
+                    rf = i
+                else:
+                    r.next = i
+                    r = r.next
+                i = i.next
+            else:
+                if not r:
+                    r = j
+                    rf = j
+                else:
+                    r.next = j
+                    r = r.next
+                j = j.next
+        return rf
+
+
+if __name__ == "__main__":
+    s = Solution()
+    # l12 = ListNode(val=4, next=None)
+    # l11 = ListNode(val=2, next=l12)
+    # l10 = ListNode(val=1, next=l11)
+    #
+    # l22 = ListNode(val=5, next=None)
+    # l21 = ListNode(val=3, next=l22)
+    # l20 = ListNode(val=1, next=l21)
+
+    l11 = ListNode(val=3, next=None)
+    l10 = ListNode(val=-9, next=l11)
+
+    l21 = ListNode(val=7, next=None)
+    l20 = ListNode(val=5, next=l21)
+
+    k = s.mergeTwoLists(list1=l10, list2=l20)
+
+    while k:
+        print(f"{k.val}")
+        k = k.next

neetcode/linked_list/merge_two_linked_lists/neetcode_solution.py

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+from typing import Optional
+
+
+# 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: ListNode, list2: ListNode) -> ListNode:
+        dummy = node = ListNode()
+
+        while list1 and list2:
+            if list1.val < list2.val:
+                node.next = list1
+                list1 = list1.next
+            else:
+                node.next = list2
+                list2 = list2.next
+            node = node.next
+
+        node.next = list1 or list2
+
+        return dummy.next
+
+
+if __name__ == "__main__":
+    s = Solution()
+    # l12 = ListNode(val=4, next=None)
+    # l11 = ListNode(val=2, next=l12)
+    # l10 = ListNode(val=1, next=l11)
+    #
+    # l22 = ListNode(val=5, next=None)
+    # l21 = ListNode(val=3, next=l22)
+    # l20 = ListNode(val=1, next=l21)
+
+    l11 = ListNode(val=3, next=None)
+    l10 = ListNode(val=-9, next=l11)
+
+    l21 = ListNode(val=7, next=None)
+    l20 = ListNode(val=5, next=l21)
+
+    k = s.mergeTwoLists(list1=l10, list2=l20)
+
+    while k:
+        print(f"{k.val}")
+        k = k.next