Update 0501.二叉搜索树中的众数.md

problems/0501.二叉搜索树中的众数.md

@@ -925,6 +925,44 @@ impl Solution {
 }
 ```
 
+迭代：
+
+```rust
+pub fn find_mode(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
+        let (mut cur, mut pre) = (root, i32::MIN);
+        let mut res = vec![];
+        let mut stack = vec![];
+        let (mut count, mut max_count) = (0, 0);
+        while !stack.is_empty() || cur.is_some() {
+            while let Some(node) = cur {
+                cur = node.borrow().left.clone();
+                stack.push(node);
+            }
+            if let Some(node) = stack.pop() {
+                if pre == i32::MIN {
+                    count = 1;
+                } else if pre == node.borrow().val {
+                    count += 1;
+                } else {
+                    count = 1;
+                }
+                match count.cmp(&max_count) {
+                    std::cmp::Ordering::Equal => res.push(node.borrow().val),
+                    std::cmp::Ordering::Greater => {
+                        max_count = count;
+                        res.clear();
+                        res.push(node.borrow().val);
+                    }
+                    _ => {}
+                }
+                pre = node.borrow().val;
+                cur = node.borrow().right.clone();
+            }
+        }
+        res
+    }
+```
+
 
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