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Efficient Algorithms for Linked List Operations

Tech Apr 24 49

Removing Nodes with Specific Values from a Linked List

To delete all nodes with value x from a linked list L:

void remove_value_nodes(LinkList *L, ElemType target) {
    Node *current = L->next, *prev = L, *temp;
    while (current) {
        if (current->value == target) {
            temp = current;
            current = current->next;
            prev->next = current;
            free(temp);
        } else {
            prev = current;
            current = current->next;
        }
    }
}

Finding and Removing the Minimum Value Node

To locate and delete the node with the minimum value:

LinkList remove_min_node(LinkList *L) {
    Node *prev = L, *current = prev->next;
    Node *min_prev = prev, *min_node = current;
    
    while (current) {
        if (current->value < min_node->value) {
            min_node = current;
            min_prev = prev;
        }
        prev = current;
        current = current->next;
    }
    
    min_prev->next = min_node->next;
    free(min_node);
    return L;
}

Reversing a Linked List In-Place

Two approaches to reverse a linked list with O(1) space:

// Method 1: Iterative reversal
LinkList reverse_list_1(LinkList L) {
    Node *current = L->next, *next_node, *reversed = NULL;
    L->next = NULL;
    
    while (current) {
        next_node = current->next;
        current->next = reversed;
        reversed = current;
        current = next_node;
    }
    
    L->next = reversed;
    return L;
}

// Method 2: Pointer manipulation
LinkList reverse_list_2(LinkList L) {
    Node *prev = NULL, *current = L->next, *next_node;
    
    while (current) {
        next_node = current->next;
        current->next = prev;
        prev = current;
        current = next_node;
    }
    
    L->next = prev;
    return L;
}

Detecting Cycles in a Linked List

Using Floyd's cycle-finding algorithm:

Node *detect_cycle(Node *head) {
    Node *slow = head, *fast = head;
    
    while (fast && fast->next) {
        slow = slow->next;
        fast = fast->next->next;
        
        if (slow == fast) {
            Node *start = head;
            while (start != slow) {
                start = start->next;
                slow = slow->next;
            }
            return start;
        }
    }
    
    return NULL;
}

Finding the Intersection Node of Two Linked Lists

Efficient approach to find common node:

Node *find_intersection(Node *headA, Node *headB) {
    int lenA = list_length(headA);
    int lenB = list_length(headB);
    
    Node *longer = lenA > lenB ? headA : headB;
    Node *shorter = lenA > lenB ? headB : headA;
    
    for (int i = 0; i < abs(lenA - lenB); i++)
        longer = longer->next;
    
    while (longer != shorter) {
        longer = longer->next;
        shorter = shorter->next;
    }
    
    return longer;
}

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