add leetcode 173

Author: lijinglin3

leetcode/0173.binary-search-tree-iterator/binary_search_tree_iterator.go

@@ -0,0 +1,56 @@
+package leetcode
+
+import . "github.com/lijinglin2019/algorithm-go/leetcode/common"
+
+type BSTIterator struct {
+	stack  []*TreeNode
+	length int
+}
+
+func Constructor(root *TreeNode) BSTIterator {
+	if root == nil {
+		return BSTIterator{}
+	}
+
+	stack := []*TreeNode{root}
+	n := root
+	for n.Left != nil {
+		stack = append(stack, n.Left)
+		n = n.Left
+	}
+
+	return BSTIterator{
+		stack:  stack,
+		length: len(stack),
+	}
+}
+
+/** @return the next smallest number */
+func (this *BSTIterator) Next() int {
+	n := this.stack[this.length-1]
+	this.stack = this.stack[:this.length-1]
+
+	tmp := n.Right
+	for tmp != nil {
+		this.stack = append(this.stack, tmp)
+		tmp = tmp.Left
+	}
+	this.length = len(this.stack)
+
+	return n.Val
+}
+
+/** @return whether we have a next smallest number */
+func (this *BSTIterator) HasNext() bool {
+	if this.length != 0 {
+		return true
+	}
+	return false
+}
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * obj := Constructor(root);
+ * param_1 := obj.Next();
+ * param_2 := obj.HasNext();
+ */

leetcode/0173.binary-search-tree-iterator/binary_search_tree_iterator_test.go

@@ -0,0 +1,21 @@
+package leetcode
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	. "github.com/lijinglin2019/algorithm-go/leetcode/common"
+)
+
+func TestConstructor(t *testing.T) {
+	assert.Equal(t, BSTIterator{}, Constructor((*TreeNode)(nil)))
+	assert.Equal(t, BSTIterator{stack: []*TreeNode{{}}, length: 1}, Constructor(&TreeNode{}))
+
+	constructor := Constructor(TreeNodeDecoder("[7, 3, 15, null, null, 9, 20]"))
+	for _, v := range []int{3, 7, 9, 15, 20} {
+		assert.Equal(t, true, constructor.HasNext())
+		assert.Equal(t, v, constructor.Next())
+	}
+	assert.Equal(t, false, constructor.HasNext())
+}