add new solutions

solutions/1/q173/solution.go

@@ -0,0 +1,65 @@
+package q173
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+type stackElem struct {
+	state uint8 // 0, 1, 2, 3
+	node  *TreeNode
+}
+
+type BSTIterator struct {
+	stack []stackElem
+	next  *TreeNode
+}
+
+func Constructor(root *TreeNode) BSTIterator {
+	return BSTIterator{stack: []stackElem{{node: root}}}
+}
+
+func (it *BSTIterator) Next() int {
+	it.findNext()
+	ret := it.next.Val
+	it.next = nil
+	return ret
+}
+
+func (it *BSTIterator) HasNext() bool {
+	it.findNext()
+	return it.next != nil
+}
+
+func (it *BSTIterator) findNext() {
+	for it.next == nil && len(it.stack) > 0 {
+		c := &it.stack[len(it.stack)-1]
+		c.state++
+
+		switch c.state - 1 {
+		case 0: // init
+			if c.node.Left != nil {
+				it.stack = append(it.stack, stackElem{node: c.node.Left})
+			}
+
+		case 1: // left processed
+			it.next = c.node
+
+		case 2: // middle processed
+			if c.node.Right != nil {
+				it.stack = append(it.stack, stackElem{node: c.node.Right})
+			}
+
+		case 3: // right processed
+			it.stack = it.stack[:len(it.stack)-1]
+		}
+	}
+}
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * obj := Constructor(root);
+ * param_1 := obj.Next();
+ * param_2 := obj.HasNext();
+ */