Finding the Intersection of Two Linked Lists in Go

Using Go to Determine the Intersection of Two Linked Lists

Linked lists are a fundamental data structure that are commonly used in computer science. They are composed of a series of nodes, each of which contains a value and a reference to the next node in the list. Linked lists are useful for storing and manipulating data because they are relatively simple to implement and can be easily modified by inserting or deleting nodes.

In this blog post, we will look at how to find the intersection of two linked lists using Go. Finding the intersection of two linked lists involves determining which nodes are common to both lists. This can be useful for a variety of purposes, such as detecting duplicates or comparing the contents of two lists.

Before we dive into the details of finding the intersection of two linked lists, let's first take a brief look at how linked lists are implemented in Go.



Implementing Linked Lists in Go

To implement a linked list in Go, we need to define two types: a node and a linked list. Here is an example of how we might define these types:



        
    type node struct {
        value int
        next  *node
    }
    
    
    type linkedList struct {
        head *node
        tail *node    
    }
    

The node type represents a single node in the linked list, and it contains a value and a reference to the next node in the list. The linkedList type represents the entire linked list and contains references to the head (the first node in the list) and the tail (the last node in the list).


Next, we can define functions for common operations such as inserting and deleting nodes. Here is an example of a function for inserting a new node at the beginning of the linked list:


        
    func (l *linkedList) insertAtHead(value int) {
        newNode := &node{value: value}
        if l.head == nil {
            l.head = newNode
            l.tail = newNode
        } else {
            newNode.next = l.head
		l.head = newNode
	}
}

This function creates a new node with the given value, and then inserts it at the beginning of the linked list. If the linked list is empty, the new node becomes both the head and the tail of the list. Otherwise, the new node is inserted as the new head, and the previous head becomes the second node in the list.


We can also define a function for deleting a node from the linked list:


        
    func (l *linkedList) delete(value int) {
        if l.head == nil {
            return
        }
    
        if l.head.value == value {
            l.head = l.head.next
            if l.head == nil {
                l.tail = nil
            }
            return
        }
    
        current := l.head
        for current.next != nil {
            if current.next.value == value {
                current.next = current.next.next
                if current.next == nil {
                    l.tail = current
                }
                return
            }
            current = current.next
        }
    }
    

This function searches the linked list for a node with the given value, and then removes it from the list. If the node to be deleted is the head of the list, the head is updated to point to the next node in the list. If the node to be deleted is the tail of the list, the tail is updated to point to the previous node.


With these basic functions in place, we are ready to start working on finding the intersection of two linked lists.


Finding the Intersection of Two Linked Lists


To find the intersection of two linked lists, we can use the following algorithm:


Iterate through the first linked list and store each node in a hash set.

Iterate through the second linked list and check each node against the hash set. If a node is found in the hash set, it is part of the intersection.

Return the intersection as a new linked list.


        
    func intersection(l1, l2 *linkedList) *linkedList {
        set := make(map[int]bool)
        result := &linkedList{}
    
        current := l1.head
        for current != nil {
            set[current.value] = true
            current = current.next
        }
    
        current = l2.head
        for current != nil {
            if set[current.value] {
                result.insertAtHead(current.value)
            }
            current = current.next
        }
    
        return result
    }    

This function takes two linked lists as arguments and returns a new linked list containing the intersection of the two lists. It works by iterating through the first linked list and adding each node to a hash set. It then iterates through the second linked list and checks each node against the hash set. If a node is found in the hash set, it is part of the intersection and is added to the result linked list.


To test this function, we can create two linked lists and call the intersection function:

        
    l1 := &linkedList{}
    l1.insertAtHead(1)
    l1.insertAtHead(2)
    l1.insertAtHead(3)
    
    l2 := &linkedList{}
    l2.insertAtHead(3)
    l2.insertAtHead(4)
    l2.insertAtHead(5)
    
    result := intersection(l1, l2)    

In this example, the result linked list will contain the single node with value 3, since it is the only node that is common to both linked lists.


Conclusion


In this blog post, we looked at how to find the intersection of two linked lists using Go. We discussed the basics of implementing linked lists in Go, and then implemented an algorithm for finding the intersection of two linked lists. By using a hash set to store the nodes of the first linked list, we were able to efficiently determine which nodes were part of the intersection.

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