Update 0102.二叉树的层序遍历.md

problems/0102.二叉树的层序遍历.md

@@ -668,29 +668,32 @@ object Solution {
 Rust:
 
 ```rust
-pub fn level_order(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<Vec<i32>> {
-    let mut ans = Vec::new();
-    let mut stack = Vec::new();
-    if root.is_none(){
-        return ans;
-    }
-    stack.push(root.unwrap());
-    while stack.is_empty()!= true{
-        let num = stack.len();
-        let mut level = Vec::new();
-        for _i in 0..num{
-            let tmp = stack.remove(0);
-            level.push(tmp.borrow_mut().val);
-            if tmp.borrow_mut().left.is_some(){
-                stack.push(tmp.borrow_mut().left.take().unwrap());
-            }
-            if tmp.borrow_mut().right.is_some(){
-                stack.push(tmp.borrow_mut().right.take().unwrap());
-            }
+use std::cell::RefCell;
+use std::collections::VecDeque;
+use std::rc::Rc;
+impl Solution {
+    pub fn level_order_bottom(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<Vec<i32>> {
+        let mut res = vec![];
+        let mut queue = VecDeque::new();
+        if root.is_some() {
+            queue.push_back(root);
         }
-        ans.push(level);
+        while !queue.is_empty() {
+            let mut temp = vec![];
+            for _ in 0..queue.len() {
+                let node = queue.pop_front().unwrap().unwrap();
+                temp.push(node.borrow().val);
+                if node.borrow().left.is_some() {
+                    queue.push_back(node.borrow().left.clone());
+                }
+                if node.borrow().right.is_some() {
+                    queue.push_back(node.borrow().right.clone());
+                }
+            }
+            res.push(temp);
+        }
+        res.into_iter().rev().collect()
     }
-    ans
 }
 ```