7.21 Insert Node at Position in Doubly Linked List

7.21.1 Problem Metadata

• Platform: Other
• Difficulty: Easy
• Tags:
• Techniques: Linked List

7.21.2 Description

Insert a value at position pos (1-indexed) in a doubly linked lc-list.

public DLLNode insertAt(DLLNode head, int pos, int val) {
    DLLNode node = new DLLNode(val);
    if (pos == 1) {
        node.next = head;
        if (head != null) head.prev = node;
        return node;
    }
    DLLNode curr = head;
    for (int i = 1; curr != null && i < pos - 1; i++) {
        curr = curr.next;
    }
    if (curr == null) return head;
    node.next = curr.next;
    if (curr.next != null) curr.next.prev = node;
    curr.next = node;
    node.prev = curr;
    return head;
}