feat(trees): add 102_binary_tree_level_order_traversal.rs

Author: whisperpine

README.md

@@ -138,3 +138,4 @@ so that you can use `just tf TEST` command to test.
 | - | - | - |
 | 226. Invert Binary Tree | Easy | [226_invert_binary_tree.rs](./tests/226_invert_binary_tree.rs) |
 | 104. Maximum Depth of Binary Tree | Easy | [104_maximum_depth_of_binary_tree.rs](./tests/104_maximum_depth_of_binary_tree.rs) |
+| 102. Binary Tree Level Order Traversal | Medium | [102_binary_tree_level_order_traversal.rs](./tests/102_binary_tree_level_order_traversal.rs) |

tests/102_binary_tree_level_order_traversal.rs

@@ -0,0 +1,63 @@
+// 102. Binary Tree Level Order Traversal
+// https://leetcode.com/problems/binary-tree-level-order-traversal/description/
+// Topics: Trees.
+// Difficulty: Medium.
+
+#[test]
+fn test_102_binary_tree_level_order_traversal() {}
+
+#[derive(Debug)]
+pub struct Solution;
+
+// 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,
+        }
+    }
+}
+
+// ---------------------------------
+// copy to leetcode starts from here
+// ---------------------------------
+
+use std::cell::RefCell;
+use std::collections::VecDeque;
+use std::rc::Rc;
+
+impl Solution {
+    pub fn level_order(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<Vec<i32>> {
+        let mut result: Vec<Vec<i32>> = vec![];
+        let mut vd = VecDeque::new();
+        if let Some(r) = root {
+            vd.push_back(r);
+        }
+        while !vd.is_empty() {
+            let mut row: Vec<i32> = vec![];
+            for _ in 0..vd.len() {
+                // `vd` is not empty, thus `unwrap()` is fine here.
+                let node = vd.pop_front().unwrap();
+                row.push(node.borrow().val);
+                if let Some(left) = node.borrow_mut().left.take() {
+                    vd.push_back(left);
+                }
+                if let Some(right) = node.borrow_mut().right.take() {
+                    vd.push_back(right);
+                }
+            }
+            result.push(row);
+        }
+        result
+    }
+}