add solutions

Author: hanksudo

203-remove-linked-list-elements.py

@@ -0,0 +1,24 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def removeElements(self, head: ListNode, val: int) -> ListNode:
+        while True:
+            if head is None:
+                return head
+
+            if head.val != val:
+                break
+            head = head.next
+
+        current = head
+        while current.next:
+            if current.next.val == val:
+                current.next = current.next.next
+            else:
+                current = current.next
+
+        return head

21-merge-two-sorted-lists.py

@@ -0,0 +1,27 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
+        dummy = ListNode(0)
+        tail = dummy
+        while True:
+            if l1 is None:
+                tail.next = l2
+                break
+            if l2 is None:
+                tail.next = l1
+                break
+
+            if l1.val <= l2.val:
+                tail.next = l1
+                l1 = l1.next
+            else:
+                tail.next = l2
+                l2 = l2.next
+            tail = tail.next
+
+        return dummy.next

237-delete-node-in-a-linked-list.py

@@ -0,0 +1,14 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def deleteNode(self, node):
+        """
+        :type node: ListNode
+        :rtype: void Do not return anything, modify node in-place instead.
+        """
+        node.val = node.next.val
+        node.next = node.next.next

83-remove-duplicates-from-sorted-list.py

@@ -0,0 +1,18 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def deleteDuplicates(self, head: ListNode) -> ListNode:
+        if head is None:
+            return head
+
+        current = head
+        while current.next:
+            if current.val == current.next.val:
+                current.next = current.next.next
+            else:
+                current = current.next
+        return head