Swap Nodes of Linked List without Copying

C++ Code:

void swap_nodes(Node **headPtr, int a, int b){

    if(a == b || !headPtr || !(*headPtr))

        return;

    

    Node *curr = *headPtr;

    Node *prev = nullptr;

    Node *nodeA = nullptr;

    Node *nodeB = nullptr;

    Node *prevA = nullptr;

    Node *prevB = nullptr;

    

    while (curr) {

        if(curr->data == a){

            nodeA = curr;

            prevA = prev;

        } else if(curr->data == b){

            nodeB = curr;

            prevB = prev;

        }

        prev = curr;

        curr = curr->next;

    }

    

    if(!nodeA || !nodeB)

        return;

    

    if(prevA){

        prevA->next = nodeB;

    } else { // nodeA is head

        *headPtr = nodeB;

    }

    

    if(prevB){

        prevB->next = nodeA;

    } else { // nodeB is head

        *headPtr = nodeA;

    }

    

    Node *tmp = nodeA->next;

    nodeA->next = nodeB->next;

    nodeB->next = tmp;

}

Detailed explanation is available on youtube:  

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