Method getNodeByRank

structure/zset.go:445–473

getNodeByRank is a method of the SkipList type that is used to retrieve a node based on its rank within the list. The method takes as argument an integer rank and returns a pointer to the SkipListNode at the specified rank, or nil if there is no such node. First, the method initializes a variable t

(rank int)

// If during the traversal the cumulative span equals the target rank, the method returns the getNodeByRank node.
// If the end of the SkipList is reached, or the target rank isn't found on any level, the method returns nil.
func (sl *SkipList) getNodeByRank(rank int) *SkipListNode {
	// This variable is used to keep track of the number of nodes we have
	// traversed while going through the levels of the SkipList.
	var traversed int

	// Define a SkipListNode pointer h, initialized with sl.head
	// At the start, this pointer is set to head node of the SkipList.
	h := sl.head

	// The outer loop decrements levels from highest level to lowest.
	for i := sl.level - 1; i >= 0; i-- {

		// The inner loop traverses the nodes at current level while the next node isn't null and we haven't traversed beyond the 'rank'.
		// The traversed variable is also updated to include the span of the current level.
		for h.level[i].next != nil && (traversed+h.level[i].span) <= rank {
			traversed += h.level[i].span
			h = h.level[i].next
		}

		// If traversed equals 'rank', it means we've found the node at the rank we are looking for.
		// So, return the node.
		if traversed == rank {
			return h
		}
	}

	// If the node at 'rank' wasn't found in the SkipList, return nil.
	return nil
}

// ZAdd adds a value with its given score and member to a sorted set (ZSet), associated with
// the provided key. It is a method on the ZSetStructure type.