diff --git a/README.md b/README.md
index 812a477..90e688b 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ import (
 )
 
 func main() {
-    pq := pqueuekey.New(compare.Int)
+    pq := New(compare.Int)
     pq.Push(1, 1)
     pq.Push(4, 4)
     pq.Push(5, 5)
@@ -40,14 +40,15 @@ func main() {
     log.Println(values3)
 
     iter := pq.Iterator() // Next 大到小 从root节点起始
+    log.Println(pq.String())
     // log.Println(iter.Value()) 直接使用会报错,
     iter.ToHead()
-    log.Println(iter.Value()) // 起始最大值. true 5
+    iter.Next()
+    log.Println(iter.Value())              // 起始最大值. true 5
     log.Println(iter.Prev(), iter.Value()) // false 5
 
     // Prev 大到小
     log.Println(iter.Next(), iter.Value()) // true 4
-    
-    
+
 }
 ```
diff --git a/priority_queue/iterator.go b/priority_queue/iterator.go
index 1f6efc4..ecc74e7 100644
--- a/priority_queue/iterator.go
+++ b/priority_queue/iterator.go
@@ -1,7 +1,7 @@
 package pqueue
 
 import (
-	"github.com/474420502/focus/stack/listarraystack"
+	lastack "github.com/474420502/focus/stack/listarraystack"
 )
 
 type Iterator struct {
@@ -31,13 +31,36 @@ func NewIteratorWithCap(n *Node, cap int) *Iterator {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) GetNode() *Node {
diff --git a/priority_queue/priority_queue_test.go b/priority_queue/priority_queue_test.go
index 2375e59..56c02ad 100644
--- a/priority_queue/priority_queue_test.go
+++ b/priority_queue/priority_queue_test.go
@@ -283,13 +283,15 @@ func TestPriorityQueue_Iterator(t *testing.T) {
 
 	values := pq.Values()
 	for i := 0; ; i++ {
+
+		if !iter.Next() {
+			break
+		}
+
 		if values[i] != iter.Value() {
 			t.Error(values[i], " != ", iter.Value())
 		}
 
-		if !iter.Prev() {
-			break
-		}
 	}
 }
 
diff --git a/priority_queuekey/iterator.go b/priority_queuekey/iterator.go
index 2174357..94a3215 100644
--- a/priority_queuekey/iterator.go
+++ b/priority_queuekey/iterator.go
@@ -31,13 +31,36 @@ func NewIteratorWithCap(n *Node, cap int) *Iterator {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) GetNode() *Node {
diff --git a/priority_queuekey/priority_queuekey_test.go b/priority_queuekey/priority_queuekey_test.go
index ce96b71..f26c10d 100644
--- a/priority_queuekey/priority_queuekey_test.go
+++ b/priority_queuekey/priority_queuekey_test.go
@@ -387,13 +387,15 @@ func TestPriorityQueue_Iterator(t *testing.T) {
 
 	values := pq.Values()
 	for i := 0; ; i++ {
-		if values[i] != iter.Value() {
-			t.Error(values[i], " != ", iter.Value())
-		}
 
 		if !iter.Next() {
 			break
 		}
+
+		if values[i] != iter.Value() {
+			t.Error(values[i], " != ", iter.Value())
+		}
+
 	}
 }
 
@@ -481,10 +483,10 @@ func TestMain(t *testing.T) {
 	log.Println(pq.String())
 	// log.Println(iter.Value()) 直接使用会报错,
 	iter.ToHead()
+	iter.Next()
 	log.Println(iter.Value())              // 起始最大值. true 5
 	log.Println(iter.Prev(), iter.Value()) // false 5
 
 	// Prev 大到小
 	log.Println(iter.Next(), iter.Value()) // true 4
-
 }
diff --git a/set/treeset/treeset_test.go b/set/treeset/treeset_test.go
index 5c2254a..0bf5312 100644
--- a/set/treeset/treeset_test.go
+++ b/set/treeset/treeset_test.go
@@ -152,7 +152,14 @@ func TestTreeSet_Iterator(t *testing.T) {
 
 	iter := set.Iterator()
 	iter.ToHead()
-	// 3 4 5
+
+	// if not call Next Prev will error
+	// 5 4 3
+	// if iter.Value() != nil {
+	// 	t.Error(iter.Value())
+	// }
+
+	iter.Next()
 	if iter.Value() != 3 {
 		t.Error(iter.Value())
 	}
@@ -162,12 +169,8 @@ func TestTreeSet_Iterator(t *testing.T) {
 		t.Error(iter.Value())
 	}
 
-	iter.Next()
-	if iter.Value() != 5 {
-		t.Error(iter.Value())
-	}
-
 	iter.ToTail()
+	iter.Prev()
 	if iter.Value() != 5 {
 		t.Error(iter.Value())
 	}
@@ -176,4 +179,16 @@ func TestTreeSet_Iterator(t *testing.T) {
 	if iter.Value() != 4 {
 		t.Error(iter.Value())
 	}
+
+	iter.ToHead()
+	iter.Prev()
+	if iter.Value() != 3 {
+		t.Error(iter.Value())
+	}
+
+	iter.ToTail()
+	iter.Next()
+	if iter.Value() != 5 {
+		t.Error(iter.Value())
+	}
 }
diff --git a/tree/avl/avl_test.go b/tree/avl/avl_test.go
index 0192966..e86abed 100644
--- a/tree/avl/avl_test.go
+++ b/tree/avl/avl_test.go
@@ -49,11 +49,13 @@ func TestIteratorHeadTail(t *testing.T) {
 	}
 
 	iter.ToHead()
+	iter.Prev() // or iter.Next
 	if iter.Value() != 1 {
 		t.Error("iter.Value() != ", 14, " value =", iter.Value())
 	}
 
 	iter.ToTail()
+	iter.Next() // or iter.Prev()
 	if iter.Value() != 30 {
 		t.Error("iter.Value() != ", 30, " value =", iter.Value())
 	}
diff --git a/tree/avl/iterator.go b/tree/avl/iterator.go
index 926c60a..41f832c 100644
--- a/tree/avl/iterator.go
+++ b/tree/avl/iterator.go
@@ -1,7 +1,7 @@
 package avl
 
 import (
-	"github.com/474420502/focus/stack/listarraystack"
+	lastack "github.com/474420502/focus/stack/listarraystack"
 )
 
 type Iterator struct {
@@ -31,13 +31,36 @@ func NewIteratorWithCap(n *Node, cap int) *Iterator {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) GetNode() *Node {
diff --git a/tree/avldup/iterator.go b/tree/avldup/iterator.go
index d802dce..864fae2 100644
--- a/tree/avldup/iterator.go
+++ b/tree/avldup/iterator.go
@@ -1,7 +1,7 @@
 package avldup
 
 import (
-	"github.com/474420502/focus/stack/listarraystack"
+	lastack "github.com/474420502/focus/stack/listarraystack"
 )
 
 type Iterator struct {
@@ -31,13 +31,36 @@ func NewIteratorWithCap(n *Node, cap int) *Iterator {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) GetNode() *Node {
diff --git a/tree/avlkey/iterator.go b/tree/avlkey/iterator.go
index 943fa05..b74ba8d 100644
--- a/tree/avlkey/iterator.go
+++ b/tree/avlkey/iterator.go
@@ -31,13 +31,36 @@ func NewIteratorWithCap(n *Node, cap int) *Iterator {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) GetNode() *Node {
diff --git a/tree/avlkeydup/iterator.go b/tree/avlkeydup/iterator.go
index 3c897b0..c7b054c 100644
--- a/tree/avlkeydup/iterator.go
+++ b/tree/avlkeydup/iterator.go
@@ -31,13 +31,36 @@ func NewIteratorWithCap(n *Node, cap int) *Iterator {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) GetNode() *Node {
diff --git a/tree/vbt/iterator.go b/tree/vbt/iterator.go
index 1bedc99..8a38ac6 100644
--- a/tree/vbt/iterator.go
+++ b/tree/vbt/iterator.go
@@ -31,13 +31,36 @@ func NewIteratorWithCap(n *Node, cap int) *Iterator {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) GetNode() *Node {
diff --git a/tree/vbtdupkey/iterator.go b/tree/vbtdupkey/iterator.go
index 5d545a6..afafeb8 100644
--- a/tree/vbtdupkey/iterator.go
+++ b/tree/vbtdupkey/iterator.go
@@ -47,6 +47,7 @@ func (iter *Iterator) ToHead() {
 		iter.cur = iter.cur.children[0]
 	}
 	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
@@ -63,6 +64,7 @@ func (iter *Iterator) ToTail() {
 		iter.cur = iter.cur.children[1]
 	}
 	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) SetNode(n *Node) {
diff --git a/tree/vbtdupkey/vbtdupkey_test.go b/tree/vbtdupkey/vbtdupkey_test.go
index a584349..22f7166 100644
--- a/tree/vbtdupkey/vbtdupkey_test.go
+++ b/tree/vbtdupkey/vbtdupkey_test.go
@@ -34,12 +34,13 @@ func TestIteratorHeadTail(t *testing.T) {
 
 	iter := tree.Iterator()
 	iter.ToHead() // 从小到大
+	iter.Next()
 	if iter.Value() != 1 {
 		t.Error("value error", iter.Value())
 	}
 
 	iter.ToTail()
-
+	iter.Prev()
 	if iter.Value() != 100 {
 		t.Error("value error", iter.Value())
 	}
@@ -57,6 +58,7 @@ func TestIteratorHeadTail(t *testing.T) {
 
 		iter = tree.Iterator()
 		iter.ToTail()
+		iter.Prev()
 		if iter.Value() != result[0] {
 			t.Error("ToTail error", result, iter.Value())
 		}
@@ -64,6 +66,7 @@ func TestIteratorHeadTail(t *testing.T) {
 		result = tree.GetAround(-1)
 
 		iter.ToHead()
+		iter.Next()
 		if iter.Value() != result[2] {
 			t.Error("ToTail error", result, iter.Value())
 		}
diff --git a/tree/vbtkey/iterator.go b/tree/vbtkey/iterator.go
index 556eb4a..28f5327 100644
--- a/tree/vbtkey/iterator.go
+++ b/tree/vbtkey/iterator.go
@@ -35,13 +35,36 @@ func (iter *Iterator) GetNode() *Node {
 }
 
 func (iter *Iterator) ToHead() {
-	for iter.Prev() {
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[0] != nil {
+		iter.cur = iter.cur.children[0]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) ToTail() {
-	for iter.Next() {
+
+	if iter.cur == nil {
+		iter.cur = iter.up
 	}
+
+	for iter.cur.parent != nil {
+		iter.cur = iter.cur.parent
+	}
+
+	for iter.cur.children[1] != nil {
+		iter.cur = iter.cur.children[1]
+	}
+	iter.SetNode(iter.cur)
+	iter.cur = nil
 }
 
 func (iter *Iterator) SetNode(n *Node) {