implemented singly-linked list in Python

python/06_linkedlist/singly_linked_list.py

@@ -0,0 +1,139 @@
+"""
+    1) Insertion, deletion and search of singly-linked list;
+    2) Assumes int type for data in list nodes.
+
+    Author: Wenru
+"""
+from typing import Optional
+
+class Node:
+    
+    def __init__(self, data: int, next=None):
+        self.data = data
+        self._next = next
+    
+
+class SinglyLinkedList:
+
+    def __init__(self):
+        self._head = None
+    
+    def find_by_value(self, value: int) -> Optional[Node]:
+        p = self._head
+        while p and p.data != value:
+            p = p._next
+        
+        return p
+
+    def find_by_index(self, index: int) -> Optional[Node]:
+        p = self._head
+        position = 0
+        while p and position != index:
+            p = p._next
+            position += 1
+        
+        return p
+
+    def insert_value_to_head(self, value: int):
+        new_node = Node(value)
+        self.insert_node_to_head(new_node)
+    
+    def insert_node_to_head(self, new_node: Node):
+        if new_node:
+            new_node._next = self._head
+            self._head = new_node
+    
+    def insert_value_after(self, node: Node, value: int):
+        new_node = Node(value)
+        self.insert_node_after(node, new_node)
+    
+    def insert_node_after(self, node: Node, new_node: Node):
+        if not node or not new_node:
+            return
+        new_node._next = node._next
+        node._next = new_node
+
+    def insert_value_before(self, node: Node, value: int):
+        new_node = Node(value)
+        self.insert_node_before(node, new_node)
+
+    def insert_node_before(self, node: Node, new_node: Node):
+        if not self._head or not node or not new_node:
+            return
+        if self._head == node:
+            self.insert_node_to_head(new_node)
+            return
+        current = self._head
+        while current._next and current._next != node:
+            current = current._next
+        if not current._next:   # node is not even in the list
+            return
+        new_node._next = node
+        current._next = new_node
+
+    def delete_by_node(self, node: Node):
+        if not self._head or not node:
+            return
+        if node._next:
+            node.data = node._next.data
+            node._next = node._next._next
+            return
+        # node is the last one or not in the list
+        current = self._head
+        while current and current._next != node:
+            current = current._next
+        if not current:  # node not in the list
+            return 
+        current._next = None
+
+    def delete_by_value(self, value: int):
+        if not self._head or not value:
+            return
+        fake_head = Node(value+1)
+        fake_head._next = self._head
+        prev, current = fake_head, self._head
+        while current:
+            if current.data != value:
+                prev._next = current
+                prev = prev._next
+            current = current._next
+        if prev._next:
+            prev._next = None
+        self._head = fake_head._next  # in case head.data == value
+    
+    def __repr__(self) -> str:
+        nums = []
+        current = self._head
+        while current:
+            nums.append(current.data)
+            current = current._next
+        if len(nums) > 0:
+            return "->".join(str(num) for num in nums)
+        else:
+            return ""
+
+    def print_all(self):
+        current = self._head
+        if current:
+            print(f"{current.data}", end="")
+            current = current._next
+        while current:
+            print(f"->{current.data}", end="")
+            current = current._next
+        print("\n", flush=True)
+
+
+if __name__ == "__main__":
+    l = SinglyLinkedList()
+    for i in range(15):
+        l.insert_value_to_head(i)
+    node9 = l.find_by_value(9)
+    l.insert_value_before(node9, 20)
+    l.insert_value_before(node9, 16)
+    l.insert_value_before(node9, 16)
+    l.delete_by_value(16)
+    node11 = l.find_by_index(3)
+    l.delete_by_node(node11)
+    l.delete_by_node(l._head)
+    l.delete_by_value(13)
+    print(l)