How to implement skip table data structure in golang

Skip list is a data structure based on linked list, similar to balanced tree, which can realize fast search, insertion and deletion operations. The skip list was proposed by William Pugh in 1990. Its implementation is based on the linked list, and multi-level indexes are added on the basis of the linked list, so that the nodes of the linked list can be quickly located through the index. The linked list at the bottom of the jump list can be a one-way linked list, a doubly linked list, etc., but the most commonly used one is a one-way linked list. This article mainly introduces how to use Golang language to implement skip table data structure.

Structure of skip list

The main structure of skip list consists of three parts: head node, array and linked list. The head node is used to locate the starting node of the jump list. Arrays are used to store multi-level indexes. Each element of the array is a pointer to a linked list node. Linked list is the core of skip list and is used to store data.

Each level of the jump list contains some nodes, and the nodes are connected to each other through pointers. The number of nodes on each level gradually decreases. The lowest layer contains all data nodes. This layer is usually called the "base layer", also known as the "level 0 linked list". Each node is either a data node or an index node. The index node points to the next level node, and there can be up to logn level indexes, where n is the number of data nodes. If there is a k-level index, then the node at the i-th level index will make every 2^i nodes of the i-1-th level index node point to the node at the i-th level index. Each node contains a pointer to the next level node at the same location.

Golang implements skip table

To implement the skip table data structure in Golang language, you mainly need to implement the following functions.

1. createNode function: Responsible for creating jump table nodes.

type skipNode struct {

forward []*skipNode 
key int
val interface{}

}

func createNode(level int, key int, val interface{}) *skipNode {

return &skipNode{
    forward: make([]*skipNode, level),
    key: key,
    val: val,
}

}

2. insert function: Responsible for inserting data into the jump table.

func (list *SkipList) insert(key int, val interface{}, level int) {

 update := make([]*skipNode, list.level+1)
 currentNode := list.head
 for i := list.level; i >= 0; i-- {
    for currentNode.forward[i] != nil && currentNode.forward[i].key < key {
        currentNode = currentNode.forward[i]
    }
    update[i] = currentNode
 }
 currentNode = currentNode.forward[0]
 if currentNode != nil && currentNode.key == key {
    currentNode.val = val
 } else {
    newNode := createNode(level, key, val)
    for i := 0; i <= level; i++ {
        newNode.forward[i] = update[i].forward[i]
        update[i].forward[i] = newNode
    }
 }

}

3. delete function: responsible delete data.

func (list *SkipList) delete(key int) {

update := make([]*skipNode, list.level+1)
currentNode := list.head

for i := list.level; i >= 0; i-- {
    for currentNode.forward[i] != nil && currentNode.forward[i].key < key {
        currentNode = currentNode.forward[i]
    }
    update[i] = currentNode
}

currentNode = currentNode.forward[0]
if currentNode != nil && currentNode.key == key {
    for i := 0; i <= list.level; i++ {
        if update[i].forward[i] != currentNode {
            break
        }
        update[i].forward[i] = currentNode.forward[i]
    }
}

}

4. find function: Responsible for finding data in the skip list.

func (list SkipList) find(key int) skipNode {

currentNode := list.head
for i := list.level; i >= 0; i-- {
    for currentNode.forward[i] != nil && currentNode.forward[i].key < key {
        currentNode = currentNode.forward[i]
    }
}
currentNode = currentNode.forward[0]
if currentNode != nil && currentNode.key == key {
    return currentNode
} else {
    return nil
}

}

The above are the main requirements to implement the skip list function. In addition, a SkipList structure needs to be implemented, which contains some attributes of the skip list, such as the head node, maximum depth, etc.

Conclusion

The skip table is an efficient data structure that can implement insertion, deletion and search operations with an average O(log n) time complexity. The Golang language provides a relatively friendly syntax and standard library, so it is relatively simple to implement jump tables using the Golang language. By studying this article, I believe that readers will not only have a deeper understanding of skip tables, but also master the implementation method of skip tables in Golang language.

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