treemap: add new API ReverseRange for iterating TreeMap in Reverse Order

pkg/treemap/custom.go

@@ -89,3 +89,15 @@ func (m *TreeMap[K, V]) Range(f func(key K, value V) bool) {
 		}
 	}
 }
+
+// ReverseRange calls f sequentially in reverse order for each key and value
+// present in the map. If f returns false, range stops the iteration.
+func (m *TreeMap[K, V]) ReverseRange(f func(key K, value V) bool) {
+	iterator := m.Iterator()
+	iterator.End()
+	for iterator.Prev() {
+		if !f(iterator.Key(), iterator.Value()) {
+			break
+		}
+	}
+}

pkg/treemap/custom_test.go

@@ -0,0 +1,35 @@
+package treemap
+
+import "testing"
+
+func TestMapRange(t *testing.T) {
+	m := New[int, string]()
+
+	m.Put(5, "e")
+	m.Put(6, "f")
+	m.Put(7, "g")
+	m.Put(3, "c")
+	m.Put(4, "d")
+	m.Put(1, "x")
+	m.Put(2, "b")
+
+	expectedKey := 1
+	m.Range(func(key int, value string) bool {
+		if key != expectedKey {
+			t.Errorf("[Range] expected %d, got %d", expectedKey, key)
+			return false
+		}
+		expectedKey++
+		return true
+	})
+
+	expectedKey = 7
+	m.ReverseRange(func(key int, value string) bool {
+		if key != expectedKey {
+			t.Errorf("[ReverseRange] expected %d, got %d", expectedKey, key)
+			return false
+		}
+		expectedKey--
+		return true
+	})
+}