add radix package start

bs_radix/bs_radix.go

@@ -0,0 +1,330 @@
+package bs_radix
+
+import (
+	"sort"
+	"strings"
+	"fmt"
+)
+
+
+// leafNode is used to represent a value
+type leafNode struct {
+	key string
+	val interface{}
+}
+
+// edge is used to represent an edge node
+type edge struct {
+	label byte
+	node  *node
+}
+
+type node struct {
+	// leaf is used to store possible leaf
+	leaf *leafNode
+
+	// prefix is the common prefix we ignore
+	prefix string
+
+	// Edges should be stored in-order for iteration.
+	// We avoid a fully materialized slice to save memory,
+	// since in most cases we expect to be sparse
+	edges edges
+}
+
+func (n *node) isLeaf() bool {
+	return n.leaf != nil
+}
+
+func (n *node) addEdge(e edge) {
+	n.edges = append(n.edges, e)
+	n.edges.Sort()
+}
+
+func (n *node) replaceEdge(e edge) {
+	num := len(n.edges)
+	idx := sort.Search(num, func(i int) bool {
+		return n.edges[i].label >= e.label
+	})
+	if idx < num && n.edges[idx].label == e.label {
+		n.edges[idx].node = e.node
+		return
+	}
+	panic("replacing missing edge")
+}
+
+func (n *node) getEdge(label byte) *node {
+	num := len(n.edges)
+	idx := sort.Search(num, func(i int) bool {
+		return n.edges[i].label >= label
+	})
+	if idx < num && n.edges[idx].label == label {
+		return n.edges[idx].node
+	}
+	return nil
+}
+
+func (n *node) delEdge(label byte) {
+	num := len(n.edges)
+	idx := sort.Search(num, func(i int) bool {
+		return n.edges[i].label >= label
+	})
+	if idx < num && n.edges[idx].label == label {
+		copy(n.edges[idx:], n.edges[idx+1:])
+		n.edges[len(n.edges)-1] = edge{}
+		n.edges = n.edges[:len(n.edges)-1]
+	}
+}
+
+type edges []edge
+
+func (e edges) Len() int {
+	return len(e)
+}
+
+func (e edges) Less(i, j int) bool {
+	return e[i].label < e[j].label
+}
+
+func (e edges) Swap(i, j int) {
+	e[i], e[j] = e[j], e[i]
+}
+
+func (e edges) Sort() {
+	sort.Sort(e)
+}
+
+// Tree implements a radix tree. This can be treated as a
+// Dictionary abstract data type. The main advantage over
+// a standard hash map is prefix-based lookups and
+// ordered iteration,
+type Tree struct {
+	root *node
+	size int
+}
+
+// New returns an empty Tree
+func New() *Tree {
+	t := &Tree{root: &node{}}
+	return t
+}
+
+// Len is used to return the number of elements in the tree
+func (t *Tree) Len() int {
+	return t.size
+}
+
+// longestPrefix finds the length of the shared prefix
+// of two strings
+func longestPrefix(k1, k2 string) int {
+	max := len(k1)
+	if l := len(k2); l < max {
+		max = l
+	}
+	var i int
+	for i = 0; i < max; i++ {
+		if k1[i] != k2[i] {
+			break
+		}
+	}
+	return i
+}
+
+// Insert is used to add a newentry or update
+// an existing entry. Returns if updated.
+func (t *Tree) Insert(s string, v interface{}) (interface{}, bool) {
+	var parent *node
+	n := t.root
+	search := s
+	for {
+		// Handle key exhaution
+		if len(search) == 0 {
+			if n.isLeaf() {
+				old := n.leaf.val
+				n.leaf.val = v
+				return old, true
+			}
+
+			n.leaf = &leafNode{
+				key: s,
+				val: v,
+			}
+			t.size++
+			return nil, false
+		}
+
+		// Look for the edge
+		parent = n
+		n = n.getEdge(search[0])
+
+		// No edge, create one
+		if n == nil {
+			e := edge{
+				label: search[0],
+				node: &node{
+					leaf: &leafNode{
+						key: s,
+						val: v,
+					},
+					prefix: search,
+
+				},
+			}
+			fmt.Println("Prefix: ", search)
+			parent.addEdge(e)
+			t.size++
+			return nil, false
+		}
+
+		// Determine longest prefix of the search key on match
+		commonPrefix := longestPrefix(search, n.prefix)
+		if commonPrefix == len(n.prefix) {
+			search = search[commonPrefix:]
+			continue
+		}
+
+		// Split the node
+		t.size++
+		child := &node{
+			prefix: search[:commonPrefix],
+
+		}
+		fmt.Println("Prefix: ", search[:commonPrefix])
+		parent.replaceEdge(edge{
+			label: search[0],
+			node:  child,
+		})
+
+		// Restore the existing node
+		child.addEdge(edge{
+			label: n.prefix[commonPrefix],
+			node:  n,
+		})
+		n.prefix = n.prefix[commonPrefix:]
+		fmt.Println("Prefix: ", n.prefix[commonPrefix:])
+
+		// Create a new leaf node
+		leaf := &leafNode{
+			key: s,
+			val: v,
+		}
+
+		// If the new key is a subset, add to to this node
+		search = search[commonPrefix:]
+		if len(search) == 0 {
+			child.leaf = leaf
+			return nil, false
+		}
+
+		// Create a new edge for the node
+		child.addEdge(edge{
+			label: search[0],
+			node: &node{
+				leaf:   leaf,
+				prefix: search,
+
+			},
+
+		})
+		fmt.Println("Prefix: ", search)
+		return nil, false
+	}
+}
+
+// Delete is used to delete a key, returning the previous
+// value and if it was deleted
+func (t *Tree) Delete(s string) (interface{}, bool) {
+	var parent *node
+	var label byte
+	n := t.root
+	search := s
+	for {
+		// Check for key exhaution
+		if len(search) == 0 {
+			if !n.isLeaf() {
+				break
+			}
+			goto DELETE
+		}
+
+		// Look for an edge
+		parent = n
+		label = search[0]
+		n = n.getEdge(label)
+		if n == nil {
+			break
+		}
+
+		// Consume the search prefix
+		if strings.HasPrefix(search, n.prefix) {
+			search = search[len(n.prefix):]
+		} else {
+			break
+		}
+	}
+	return nil, false
+
+DELETE:
+	// Delete the leaf
+	leaf := n.leaf
+	n.leaf = nil
+	t.size--
+
+	// Check if we should delete this node from the parent
+	if parent != nil && len(n.edges) == 0 {
+		parent.delEdge(label)
+	}
+
+	// Check if we should merge this node
+	if n != t.root && len(n.edges) == 1 {
+		n.mergeChild()
+	}
+
+	// Check if we should merge the parent's other child
+	if parent != nil && parent != t.root && len(parent.edges) == 1 && !parent.isLeaf() {
+		parent.mergeChild()
+	}
+
+	return leaf.val, true
+}
+
+func (n *node) mergeChild() {
+	e := n.edges[0]
+	child := e.node
+	n.prefix = n.prefix + child.prefix
+	n.leaf = child.leaf
+	n.edges = child.edges
+}
+
+// Get is used to lookup a specific key, returning
+// the value and if it was found
+func (t *Tree) Get(s string) (interface{}, bool) {
+	n := t.root
+	search := s
+	for {
+		// Check for key exhaution
+		if len(search) == 0 {
+			if n.isLeaf() {
+				return n.leaf.val, true
+			}
+			break
+		}
+
+		// Look for an edge
+		n = n.getEdge(search[0])
+		if n == nil {
+			break
+		}
+
+		// Consume the search prefix
+		if strings.HasPrefix(search, n.prefix) {
+			search = search[len(n.prefix):]
+		} else {
+			break
+		}
+	}
+	return nil, false
+}
+
+
+