diff --git a/avltree/avltree.go b/avltree/avltree.go
index b822946..c2e1ff7 100644
--- a/avltree/avltree.go
+++ b/avltree/avltree.go
@@ -36,35 +36,14 @@ func New(comparator utils.Comparator) *AVLTree {
 	return &AVLTree{comparator: comparator}
 }
 
-func (avl *AVLTree) replace(old *Node, newN *Node) {
-
-	if old.parent == nil {
-		setChild(newN, 0, old.children[0])
-		setChild(newN, 1, old.children[1])
-
-		newN.parent = nil
-		newN.child = -1
-		newN.height = old.height
-
-		avl.root = newN
-	} else {
-
-		setChild(newN, 0, old.children[0])
-		setChild(newN, 1, old.children[1])
-
-		newN.parent = old.parent
-		newN.child = old.child
-		newN.height = old.height
-		old.parent.children[old.child] = newN
+func (avl *AVLTree) String() string {
+	if avl.size == 0 {
+		return ""
 	}
-}
+	str := "AVLTree" + "\n"
+	output(avl.root, "", true, &str)
 
-func setChild(p *Node, child int, node *Node) {
-	p.children[child] = node
-	if node != nil {
-		node.child = child
-		node.parent = p
-	}
+	return str
 }
 
 func (avl *AVLTree) Remove(v interface{}) *Node {
@@ -195,14 +174,41 @@ func (avl *AVLTree) Put(v interface{}) {
 
 }
 
-func (avl *AVLTree) String() string {
-	if avl.size == 0 {
-		return ""
-	}
-	str := "AVLTree" + "\n"
-	output(avl.root, "", true, &str)
+func (avl *AVLTree) replace(old *Node, newN *Node) {
 
-	return str
+	if old.parent == nil {
+		setChild(newN, 0, old.children[0])
+		setChild(newN, 1, old.children[1])
+
+		newN.parent = nil
+		newN.child = -1
+		newN.height = old.height
+
+		avl.root = newN
+	} else {
+
+		setChild(newN, 0, old.children[0])
+		setChild(newN, 1, old.children[1])
+
+		newN.parent = old.parent
+		newN.child = old.child
+		newN.height = old.height
+		old.parent.children[old.child] = newN
+	}
+}
+
+func setChild(p *Node, child int, node *Node) {
+	p.children[child] = node
+	if node != nil {
+		node.child = child
+		node.parent = p
+	}
+}
+
+func setChildNotNil(p *Node, child int, node *Node) {
+	p.children[child] = node
+	node.child = child
+	node.parent = p
 }
 
 func (avl *AVLTree) debugString() string {
@@ -265,7 +271,7 @@ func (avl *AVLTree) lrrotate(cur *Node) *Node {
 		avl.root = rl
 		rl.parent = nil
 	} else {
-		setChild(cur.parent, cur.child, rl)
+		setChildNotNil(cur.parent, cur.child, rl)
 	}
 
 	rll := rl.children[0]
@@ -274,8 +280,8 @@ func (avl *AVLTree) lrrotate(cur *Node) *Node {
 	setChild(cur, 1, rll)
 	setChild(r, 0, rlr)
 
-	setChild(rl, 0, cur)
-	setChild(rl, 1, r)
+	setChildNotNil(rl, 0, cur)
+	setChildNotNil(rl, 1, r)
 
 	cur.height = getMaxChildrenHeight(cur) + 1
 	r.height = getMaxChildrenHeight(r) + 1
@@ -292,7 +298,7 @@ func (avl *AVLTree) rlrotate(cur *Node) *Node {
 		avl.root = lr
 		lr.parent = nil
 	} else {
-		setChild(cur.parent, cur.child, lr)
+		setChildNotNil(cur.parent, cur.child, lr)
 	}
 
 	lrr := lr.children[1]
@@ -300,8 +306,8 @@ func (avl *AVLTree) rlrotate(cur *Node) *Node {
 
 	setChild(cur, 0, lrr)
 	setChild(l, 1, lrl)
-	setChild(lr, 1, cur)
-	setChild(lr, 0, l)
+	setChildNotNil(lr, 1, cur)
+	setChildNotNil(lr, 0, l)
 
 	cur.height = getMaxChildrenHeight(cur) + 1
 	l.height = getMaxChildrenHeight(l) + 1
@@ -317,16 +323,17 @@ func (avl *AVLTree) rrotate(cur *Node) *Node {
 	setChild(cur, 0, l.children[1])
 
 	l.parent = cur.parent
-	if cur.parent != nil {
-		cur.parent.children[cur.child] = l
-	} else {
+	if cur.parent == nil {
 		avl.root = l
+	} else {
+		cur.parent.children[cur.child] = l
 	}
 	l.child = cur.child
 
-	l.children[1] = cur
-	cur.child = 1
-	cur.parent = l
+	setChildNotNil(l, 1, cur)
+	// l.children[1] = cur
+	// cur.child = 1
+	// cur.parent = l
 
 	cur.height = getMaxChildrenHeight(cur) + 1
 	l.height = getMaxChildrenHeight(l) + 1
@@ -343,18 +350,18 @@ func (avl *AVLTree) lrotate(cur *Node) *Node {
 
 	// 设置 需要旋转的节点到当前节点的 链条
 	r.parent = cur.parent
-	if cur.parent != nil {
-		cur.parent.children[cur.child] = r
-	} else {
+	if cur.parent == nil {
 		avl.root = r
+	} else {
+		cur.parent.children[cur.child] = r
 	}
 	r.child = cur.child
 
 	// 当前节点旋转到 左边的 链条
-
-	r.children[0] = cur
-	cur.child = 0
-	cur.parent = r
+	setChildNotNil(r, 0, cur)
+	// r.children[0] = cur
+	// cur.child = 0
+	// cur.parent = r
 
 	// 修复改动过的节点高度 先从低开始到高
 	cur.height = getMaxChildrenHeight(cur) + 1
@@ -368,10 +375,10 @@ func getMaxAndChildrenHeight(cur *Node) (h1, h2, maxh int) {
 	h2 = getHeight(cur.children[1])
 	if h1 > h2 {
 		maxh = h1
-		return
+	} else {
+		maxh = h2
 	}
 
-	maxh = h2
 	return
 }