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Author: whd

173 Binary Search Tree Iterator .cpp

@@ -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) {
+        insertLeft(root);
+    }
+
+    /** @return whether we have a next smallest number */
+    bool hasNext() {
+        return !s.empty();
+    }
+
+    /** @return the next smallest number */
+    int next() {
+        auto res = s.top()->val;
+        auto x = s.top();
+        s.pop();
+        if (x->right) {
+            insertLeft(x->right);
+        }
+        return res;
+    }
+private:
+    void insertLeft(TreeNode *x) {
+        while (x) {
+            s.push(x);
+            x = x->left;
+        }
+    }
+    stack<TreeNode *> s;
+};
+
+/**
+ * Your BSTIterator will be called like this:
+ * BSTIterator i = BSTIterator(root);
+ * while (i.hasNext()) cout << i.next();
+ */