LinkedList.py

class Node:
    def __init__(self, value):
        self.data = value
        self.next = None
        
class LinkedList:
    
    def __init__(self):
        self.head = None
        self.n = 0
        
    def __len__(self):
        return self.n
    
    def __str__(self):
        
        result = ''
        curr = self.head
        
        while curr != None:
            
            result = result + str(curr.data) + '->'
            curr = curr.next
            
        return result[:-2]
    
    def insert_head(self, value):
        
        new_node = Node(value)
        
        new_node.next = self.head
        self.head = new_node
        self.n += 1
        
    def insert_middle(self, after, value):
        
        new_node = Node(value)
        
        curr = self.head
        
        while curr.next != None:
            
            if curr.data == after:
                break
            
            curr = curr.next
            
        if curr.next == None:
            print("Item not found.")
            
        else:
            new_node.next = curr.next
            curr.next = new_node
            self.n += 1
            
    
    def insert_tail(self, value):
        
        new_node = Node(value)
        
        if self.head == None:
            self.head = new_node
            self.n += 1
            return
        
        curr = self.head
        
        while curr.next != None:
            curr = curr.next
            
        curr.next = new_node
        self.n += 1
        
    
    def delete_head(self):
        
        if self.head == None:
            print("Empty linked list.")
            return
        
        self.head = self.head.next
        self.n -= 1
        
        
    def delete_middle(self, value):
        
        if self.head == None:
            print("Empty linked list.")
            return
        
        if self.head.data == value:
            self.delete_head()
            return
        
        curr = self.head
        
        while curr.next != None:
            
            if curr.next.data == value:
                break
            curr = curr.next
            
        if curr.next != None:
            curr.next = curr.next.next
        else:
            print("Item not found")
        
    
    def delete_tail(self):
        
        if self.head == None:
            print("Empty linked list.")
            return
            
        if self.head.next == None:
            self.delete_head()
            return
            
        curr = self.head
        
        while curr.next.next != None:
            curr = curr.next
            
        curr.next = None
        self.n -= 1 
        
        
    def search_by_value(self, value):
        
        index = 0
        
        curr = self.head
        
        while curr != None:
            
            if curr.data == value:
                return index
            
            curr = curr.next
            index += 1
        
        return "Item not found"
    
    
    def search_by_index(self, index):
        
        pos = 0
        curr = self.head
        
        while curr != None:
            
            if pos == index:
                return curr.data
            
            curr = curr.next
            pos += 1
            
        return "Index not found."
    
    
if __name__ == "__main__":
    
    ll = LinkedList()
    
    ll.insert_head(1)
    ll.insert_head(2)
    ll.insert_head(3)
    ll.insert_tail(4)
    ll.insert_tail(5)
    ll.insert_middle(1,6)
    ll.insert_middle(2,8)
    ll.insert_middle(6,9)
    
    
    # ll.delete_head()
    # ll.delete_tail()
    # ll.delete_middle(6)
    
    print(len(ll))
    print(ll)
    
    print(ll.search_by_value(8))
    print(ll.search_by_index(5))