Create BinarySearchTreeIterator.java

Author: leo414

BinarySearchTreeIterator.java

@@ -0,0 +1,45 @@
+package leetcode;
+
+import java.util.Stack;
+
+/**
+ * Project Name : Leetcode
+ * Package Name : leetcode
+ * File Name : BinarySearchTreeIterator
+ * Creator : Leo
+ * Description : TODO
+ */
+public class BinarySearchTreeIterator {
+    /**
+     * 173. Binary Search Tree Iterator
+     *
+     * time : O(n)
+     * @param root
+     */
+
+    private TreeNode cur;
+    private Stack<TreeNode> stack;
+
+    public BinarySearchTreeIterator(TreeNode root) {
+        cur = root;
+        stack = new Stack<>();
+    }
+
+    /** @return whether we have a next smallest number */
+    public boolean hasNext() {
+        if (!stack.isEmpty() || cur != null) return true;
+        return false;
+    }
+
+    /** @return the next smallest number */
+    public int next() {
+        while (cur != null) {
+            stack.push(cur);
+            cur = cur.left;
+        }
+        cur = stack.pop();
+        int val = cur.val;
+        cur = cur.right;
+        return val;
+    }
+}