Binary Search Tree Iterator: in order traversal.

Author: DeanChensj

Medium/173_Binary-Search-Tree-Iterator .cpp

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+#include "../Header.h"
+#include  "../TreeNode.h"
+using namespace std;
+
+class BSTIterator {
+private:
+    stack<TreeNode*> fathers;
+    TreeNode *iterator;
+public:
+    BSTIterator(TreeNode *root) {
+        iterator = root;
+        if (iterator) {
+            while (iterator->left) {
+                fathers.push(iterator);
+                iterator = iterator->left;
+            }
+        }
+    }
+
+    /** @return whether we have a next smallest number */
+    bool hasNext() {
+        return iterator != nullptr;
+    }
+
+    /** @return the next smallest number */
+    int next() {
+        int val = iterator->val;
+        if (iterator->right) {
+            iterator = iterator->right;
+            while (iterator->left) {
+                fathers.push(iterator);
+                iterator = iterator->left;
+            } 
+        } 
+        else if (!fathers.empty()) {
+            iterator = fathers.top();
+            fathers.pop();
+        } else iterator = nullptr;
+        return val;
+    }
+};
+int main(int argc, char const *argv[])
+{
+  
+	return 0;
+}