Added solution of problem 173

Author: kurpenok

src/solutions/mod.rs

@@ -95,6 +95,7 @@ pub mod s0164_maximum_gap;
 pub mod s0165_compare_version_numbers;
 pub mod s0167_two_sum_ii_input_array_is_sorted;
 pub mod s0172_factorial_trailing_zeroes;
+pub mod s0173_binary_search_tree_iterator;
 pub mod s0231_power_of_two;
 pub mod s0232_implement_queue_using_stacks;
 pub mod s0234_palindrome_linked_list;

src/solutions/s0173_binary_search_tree_iterator.rs

@@ -0,0 +1,83 @@
+use std::cell::RefCell;
+use std::rc::Rc;
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct TreeNode {
+    pub val: i32,
+    pub left: Option<Rc<RefCell<TreeNode>>>,
+    pub right: Option<Rc<RefCell<TreeNode>>>,
+}
+
+impl TreeNode {
+    #[inline]
+    pub fn new(val: i32) -> Self {
+        TreeNode {
+            val,
+            left: None,
+            right: None,
+        }
+    }
+}
+
+pub struct BSTIterator {
+    stack: Vec<Rc<RefCell<TreeNode>>>,
+}
+
+impl BSTIterator {
+    pub fn new(root: Option<Rc<RefCell<TreeNode>>>) -> Self {
+        let mut iter = BSTIterator { stack: Vec::new() };
+        iter.push_left(root);
+        iter
+    }
+
+    pub fn next(&mut self) -> i32 {
+        let node = self.stack.pop().unwrap();
+
+        let val = node.borrow().val;
+        if let Some(right) = node.borrow().right.clone() {
+            self.push_left(Some(right));
+        }
+
+        val
+    }
+
+    pub fn has_next(&self) -> bool {
+        !self.stack.is_empty()
+    }
+
+    pub fn push_left(&mut self, mut node: Option<Rc<RefCell<TreeNode>>>) {
+        while let Some(n) = node {
+            self.stack.push(n.clone());
+            node = n.borrow().left.clone();
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_case_1() {
+        let mut bst_iterator: BSTIterator =
+            BSTIterator::new(Some(Rc::new(RefCell::new(TreeNode {
+                val: 7,
+                left: Some(Rc::new(RefCell::new(TreeNode::new(3)))),
+                right: Some(Rc::new(RefCell::new(TreeNode {
+                    val: 15,
+                    left: Some(Rc::new(RefCell::new(TreeNode::new(9)))),
+                    right: Some(Rc::new(RefCell::new(TreeNode::new(20)))),
+                }))),
+            }))));
+
+        assert_eq!(bst_iterator.next(), 3);
+        assert_eq!(bst_iterator.next(), 7);
+        assert_eq!(bst_iterator.has_next(), true);
+        assert_eq!(bst_iterator.next(), 9);
+        assert_eq!(bst_iterator.has_next(), true);
+        assert_eq!(bst_iterator.next(), 15);
+        assert_eq!(bst_iterator.has_next(), true);
+        assert_eq!(bst_iterator.next(), 20);
+        assert_eq!(bst_iterator.has_next(), false);
+    }
+}