btree: optimize deletion

btree/btree.go

@@ -215,17 +215,17 @@ func (n *Node) splitChild(i int, y *Node) {
 	z := newNode(y.t, y.isLeaf)
 	z.numberOfKeys = n.t - 1
 
-	// TODO: make optimisations
 	// Copy the last (t-1) keys of y to z
 	for j := 0; j < n.t-1; j++ {
 		z.keys[j] = y.keys[j+n.t]
+		if !y.isLeaf {
+			z.children[j] = y.children[j+n.t]
+		}
 	}
 
 	// Copy the last t children of y to z
 	if !y.isLeaf {
-		for j := 0; j < n.t; j++ {
-			z.children[j] = y.children[j+n.t]
-		}
+		z.children[n.t-1] = y.children[2*n.t-1]
 	}
 
 	// Reduce the number of keys in y
@@ -442,17 +442,17 @@ func (n *Node) borrowFromNext(index int) {
 	// The first key from sibling is inserted into keys[index]
 	n.keys[index] = sibling.keys[0]
 
-	// TODO: optimize loops here
 	// Moving all keys in sibling one step behind
 	for i := 1; i < sibling.numberOfKeys; i++ {
 		sibling.keys[i-1] = sibling.keys[i]
+		if !sibling.isLeaf {
+			sibling.children[i-1] = sibling.children[i]
+		}
 	}
 
 	// Moving the child pointers one step behind
 	if !sibling.isLeaf {
-		for i := 1; i <= sibling.numberOfKeys; i++ {
-			sibling.children[i-1] = sibling.children[i]
-		}
+		sibling.children[n.numberOfKeys-1] = sibling.children[n.numberOfKeys]
 	}
 
 	child.numberOfKeys++
@@ -471,25 +471,23 @@ func (n *Node) merge(index int) {
 	// Copies the keys from children[index+1] to children[index] at the end
 	for i := 0; i < sibling.numberOfKeys; i++ {
 		child.keys[i+n.t] = sibling.keys[i]
-	}
-
-	// Copies the child pointers from C[index+1] to children[index]
-	if !child.isLeaf {
-		for i := 0; i <= sibling.numberOfKeys; i++ {
+		if !child.isLeaf {
 			child.children[i+n.t] = sibling.children[i]
 		}
 	}
 
-	// Moves all keys after index in the current node one step before
-	// to fill the gap created by moving keys[index] to children[index]
-	for i := index + 1; i < n.numberOfKeys; i++ {
-		n.keys[i-1] = n.keys[i]
+	// Copies the child pointers from C[index+1] to children[index]
+	if !child.isLeaf {
+		child.children[sibling.numberOfKeys+n.t] = sibling.children[sibling.numberOfKeys]
 	}
 
+	// Moves all keys after index in the current node one step before
+	// to fill the gap created by moving keys[index] to children[index]
 	// Moves the child pointer after (index+1) in the current node one step before
 	// This action marks sibling for deletion by the GC
-	for i := index + 2; i <= n.numberOfKeys; i++ {
-		n.children[i-1] = n.children[i]
+	for i := index + 1; i < n.numberOfKeys; i++ {
+		n.keys[i-1] = n.keys[i]
+		n.children[i] = n.children[i+1]
 	}
 
 	// Updates the key count of child and the current node