Add Q173

Author: theFool32

173_BinarySearchTreeIterator/BinarySearchTreeIterator.cc

@@ -0,0 +1,45 @@
+/**
+ * Definition for binary tree
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class BSTIterator {
+public:
+    BSTIterator(TreeNode *root) {
+        while (root) {
+            s.push(root);
+            root = root->left;
+        }
+    }
+
+    /** @return whether we have a next smallest number */
+    bool hasNext() {
+        return !s.empty();
+    }
+
+    /** @return the next smallest number */
+    int next() {
+        TreeNode *t = s.top();
+        s.pop();
+        int val = t->val;
+        t = t->right;
+        while (t) {
+            s.push(t);
+            t = t->left;
+        }
+        return val;
+    }
+
+private:
+    stack<TreeNode*> s;
+};
+
+/**
+ * Your BSTIterator will be called like this:
+ * BSTIterator i = BSTIterator(root);
+ * while (i.hasNext()) cout << i.next();
+ */