2. Binary Tree Level Order Traversal

binary-tree-level-order-traversal/sunjae95.js

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+/**
+ * @description
+ * 동일한 depth를 방문해야하므로 bfs 및 트리 순회
+ *
+ * n = length of node of root
+ * time complexity: O(n)
+ * space complexity: O(n)
+ */
+var levelOrder = function (root) {
+  if (!root) return [];
+
+  const answer = [];
+  const queue = [root];
+  let queueCurrentIndex = 0;
+
+  while (queue.length > queueCurrentIndex) {
+    answer.push([]);
+    const answerLastIndex = answer.length - 1;
+    const depthEndIndex = queue.length;
+
+    while (depthEndIndex !== queueCurrentIndex) {
+      const tree = queue[queueCurrentIndex++];
+
+      answer[answerLastIndex].push(tree.val);
+      if (tree.left) queue.push(tree.left);
+      if (tree.right) queue.push(tree.right);
+    }
+  }
+
+  return answer;
+};