diff --git a/leetcode/README.md b/leetcode/README.md
index 1e4d0aa1..6388c697 100644
--- a/leetcode/README.md
+++ b/leetcode/README.md
@@ -30,6 +30,7 @@ LeetCode
 |153|[Find Minimum in Rotated Sorted Array](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/) | [C](./src/153.c)|Medium|
 |160|[Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists/) | [C](./src/160.c)|Easy|
 |169|[Majority Element](https://leetcode.com/problems/majority-element/) | [C](./src/169.c)|Easy|
+|173|[Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/) | [C](./src/173.c)|Medium|
 |203|[Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/) | [C](./src/203.c)|Easy|
 |206|[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/) | [C](./src/206.c)|Easy|
 |215|[Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/) | [C](./src/215.c)|Medium|
diff --git a/leetcode/src/173.c b/leetcode/src/173.c
new file mode 100644
index 00000000..018ea3eb
--- /dev/null
+++ b/leetcode/src/173.c
@@ -0,0 +1,70 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     struct TreeNode *left;
+ *     struct TreeNode *right;
+ * };
+ */
+
+#include <limits.h>
+
+typedef struct {
+    int *values;
+    int CurrentIndex;
+    int NumberOfNodes;
+} BSTIterator;
+
+void TraverseAndAssign(struct TreeNode *root, BSTIterator *obj) {
+    if(!root)
+        return;
+    if(root->left) 
+        TraverseAndAssign(root->left, obj);
+    obj->values[obj->CurrentIndex] = root->val;
+    obj->CurrentIndex++;
+    if(root->right)
+        TraverseAndAssign(root->right, obj);
+}
+
+int TotalNodes(struct TreeNode *root) {
+    if(!root) 
+        return 0;
+    int nodes_left = TotalNodes(root->left);
+    int nodes_right = TotalNodes(root->right);
+    return nodes_left + nodes_right + 1;
+}
+
+BSTIterator* bSTIteratorCreate(struct TreeNode* root) {
+    int n = TotalNodes(root);
+    int size = n+1;
+    printf("%d", size);
+    BSTIterator *obj = (BSTIterator*)malloc(sizeof(BSTIterator));
+    obj->values = (int*)calloc(size, sizeof(int));
+    obj->CurrentIndex = 0;
+    obj->NumberOfNodes = n;
+    obj->values[size - 1] = INT_MAX;
+    TraverseAndAssign(root, obj);
+    obj->CurrentIndex = 0;
+    return obj;
+}
+
+/** @return the next smallest number */
+int bSTIteratorNext(BSTIterator* obj) {
+    int NextValue = obj->values[obj->CurrentIndex];
+    obj->CurrentIndex++;
+    return NextValue;
+}
+
+/** @return whether we have a next smallest number */
+bool bSTIteratorHasNext(BSTIterator* obj) {
+    if(!obj->NumberOfNodes) {
+        return false;
+    }
+    printf(" Here ");
+    return (obj->values[obj->CurrentIndex] == INT_MAX) ? false : true;
+}
+
+void bSTIteratorFree(BSTIterator* obj) {
+    free(obj->values);
+    free(obj);
+}