binary tree level order traversal solution

Author: yhkee0404

binary-tree-level-order-traversal/yhkee0404.rs

@@ -0,0 +1,62 @@
+// Definition for a binary tree node.
+// #[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
+//     }
+//   }
+// }
+use std::rc::Rc;
+use std::cell::RefCell;
+
+#[derive(Clone)]
+struct QueueItem {
+    node: Option<Rc<RefCell<TreeNode>>>,
+    dist: i32,
+}
+
+impl Solution {
+    pub fn level_order(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<Vec<i32>> {
+        let mut ans: Vec<Vec<i32>> = vec![];
+        let mut queue: Vec<QueueItem> = vec![QueueItem::new(root, 0)];
+        let mut head = 0;
+        while head != queue.len() { // T(n) = S(n) = O(n)
+            let u = queue[head].clone();
+            head += 1;
+            match u.node {
+                Some(v) => {
+                    let v = v.borrow();
+                    let v_dist = u.dist + 1;
+                    if ans.len() <= u.dist as usize {
+                        ans.push(vec![]);
+                    }
+                    let mut a = ans.last_mut().unwrap();
+                    a.push(v.val);
+                    queue.push(QueueItem::new(v.left.clone(), v_dist));
+                    queue.push(QueueItem::new(v.right.clone(), v_dist));
+                },
+                None => (),
+            }
+        }
+        ans
+    }
+}
+
+impl QueueItem {
+    fn new(node: Option<Rc<RefCell<TreeNode>>>, dist: i32) -> Self {
+        QueueItem {
+            node: node,
+            dist: dist,
+        }
+    }
+}