Implement NextTo and PrevTo for all iterators and containers (index or key, forward-only or reversable)

stacks/arraystack/arraystack_test.go

@@ -6,6 +6,7 @@ package arraystack
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 )
 
@@ -232,6 +233,112 @@ func TestStackIteratorLast(t *testing.T) {
 	}
 }
 
+func TestStackIteratorNextTo(t *testing.T) {
+	// Sample seek function, i.e. string starting with "b"
+	seek := func(index int, value interface{}) bool {
+		return strings.HasSuffix(value.(string), "b")
+	}
+
+	// NextTo (empty)
+	{
+		stack := New()
+		it := stack.Iterator()
+		for it.NextTo(seek) {
+			t.Errorf("Shouldn't iterate on empty stack")
+		}
+	}
+
+	// NextTo (not found)
+	{
+		stack := New()
+		stack.Push("xx")
+		stack.Push("yy")
+		it := stack.Iterator()
+		for it.NextTo(seek) {
+			t.Errorf("Shouldn't iterate on empty stack")
+		}
+	}
+
+	// NextTo (found)
+	{
+		stack := New()
+		stack.Push("aa")
+		stack.Push("bb")
+		stack.Push("cc")
+		it := stack.Iterator()
+		it.Begin()
+		if !it.NextTo(seek) {
+			t.Errorf("Shouldn't iterate on empty stack")
+		}
+		if index, value := it.Index(), it.Value(); index != 1 || value.(string) != "bb" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 1, "bb")
+		}
+		if !it.Next() {
+			t.Errorf("Should go to first element")
+		}
+		if index, value := it.Index(), it.Value(); index != 2 || value.(string) != "aa" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 2, "aa")
+		}
+		if it.Next() {
+			t.Errorf("Should not go past last element")
+		}
+	}
+}
+
+func TestStackIteratorPrevTo(t *testing.T) {
+	// Sample seek function, i.e. string starting with "b"
+	seek := func(index int, value interface{}) bool {
+		return strings.HasSuffix(value.(string), "b")
+	}
+
+	// PrevTo (empty)
+	{
+		stack := New()
+		it := stack.Iterator()
+		it.End()
+		for it.PrevTo(seek) {
+			t.Errorf("Shouldn't iterate on empty stack")
+		}
+	}
+
+	// PrevTo (not found)
+	{
+		stack := New()
+		stack.Push("xx")
+		stack.Push("yy")
+		it := stack.Iterator()
+		it.End()
+		for it.PrevTo(seek) {
+			t.Errorf("Shouldn't iterate on empty stack")
+		}
+	}
+
+	// PrevTo (found)
+	{
+		stack := New()
+		stack.Push("aa")
+		stack.Push("bb")
+		stack.Push("cc")
+		it := stack.Iterator()
+		it.End()
+		if !it.PrevTo(seek) {
+			t.Errorf("Shouldn't iterate on empty stack")
+		}
+		if index, value := it.Index(), it.Value(); index != 1 || value.(string) != "bb" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 1, "bb")
+		}
+		if !it.Prev() {
+			t.Errorf("Should go to first element")
+		}
+		if index, value := it.Index(), it.Value(); index != 0 || value.(string) != "cc" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 0, "cc")
+		}
+		if it.Prev() {
+			t.Errorf("Should not go before first element")
+		}
+	}
+}
+
 func TestStackSerialization(t *testing.T) {
 	stack := New()
 	stack.Push("a")

stacks/arraystack/iterator.go

@@ -82,3 +82,31 @@ func (iterator *Iterator) Last() bool {
 	iterator.End()
 	return iterator.Prev()
 }
+
+// NextTo moves the iterator to the next element from current position that satisfies the condition given by the
+// passed function, and returns true if there was a next element in the container.
+// If NextTo() returns true, then next element's index and value can be retrieved by Index() and Value().
+// Modifies the state of the iterator.
+func (iterator *Iterator) NextTo(f func(index int, value interface{}) bool) bool {
+	for iterator.Next() {
+		index, value := iterator.Index(), iterator.Value()
+		if f(index, value) {
+			return true
+		}
+	}
+	return false
+}
+
+// PrevTo moves the iterator to the previous element from current position that satisfies the condition given by the
+// passed function, and returns true if there was a next element in the container.
+// If PrevTo() returns true, then next element's index and value can be retrieved by Index() and Value().
+// Modifies the state of the iterator.
+func (iterator *Iterator) PrevTo(f func(index int, value interface{}) bool) bool {
+	for iterator.Prev() {
+		index, value := iterator.Index(), iterator.Value()
+		if f(index, value) {
+			return true
+		}
+	}
+	return false
+}