Intersection of Two Linked Lists: A Simple Algorithmic Approach

Introduction

Problem Statement

Given two linked lists, find the node at which the two lists intersect. If the two linked lists do not intersect, return null.

Background Theory

Before we dive into the algorithmic approach, let's first understand some basic concepts of linked lists. A linked list is a data structure that consists of a sequence of nodes, where each node contains a value and a pointer to the next node. The last node in the list points to null, indicating the end of the list.

Algorithmic Approach

The algorithmic approach to finding the intersection of two linked lists involves the following steps:

Traverse both linked lists and calculate their lengths.
Calculate the difference in length between the two linked lists.
Traverse the longer linked list by the difference in length.
Traverse both linked lists simultaneously until the two pointers meet.
Return the node at which the two pointers meet.

Here is the implementation of the algorithm in C++:

ListNode *getIntersectionNode(ListNode *headA, ListNode *headB)
{
    ListNode *currA = headA, *currB = headB;
    int lenA = 0, lenB = 0;

    while (currA != nullptr)
    {
        lenA++;
        currA = currA->next;
    }

    while (currB != nullptr)
    {
        lenB++;
        currB = currB->next;
    }

    currA = headA;
    currB = headB;

    int diff = abs(lenA - lenB);

    if (lenA > lenB)
    {
        while (diff--)
            currA = currA->next;
    }
    else
    {
        while (diff--)
            currB = currB->next;
    }

    while (currA != currB)
    {
        currA = currA->next;
        currB = currB->next;
    }

    return currA;
}

Time Complexity

The time complexity of this algorithm is O(m+n), where m and n are the lengths of the two linked lists.

Space Complexity

The space complexity of this algorithm is O(1), as we are not using any extra space.

Conclusion

In conclusion, we have discussed a simple algorithmic approach to finding the intersection of two linked lists. This approach has a time complexity of O(m+n) and a space complexity of O(1). This algorithm is efficient and can be used in various applications that involve linked lists.

Stackable