feat: Binary Tree Level Order Traversal

Author: gwbaik9717

binary-tree-level-order-traversal/gwbaik9717.js

@@ -0,0 +1,67 @@
+// n: number of nodes
+// Time complexity: O(n)
+// Space complexity: O(n)
+
+class _Queue {
+  constructor() {
+    this.q = [];
+    this.front = 0;
+    this.rear = 0;
+  }
+
+  push(value) {
+    this.q.push(value);
+    this.rear++;
+  }
+
+  shift() {
+    const rv = this.q[this.front];
+    delete this.q[this.front++];
+    return rv;
+  }
+
+  isEmpty() {
+    return this.front === this.rear;
+  }
+}
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[][]}
+ */
+var levelOrder = function (root) {
+  const answer = [];
+  const q = new _Queue();
+
+  if (root) {
+    q.push([root, 0]);
+  }
+
+  while (!q.isEmpty()) {
+    const [current, lv] = q.shift();
+
+    if (answer.at(lv) === undefined) {
+      answer[lv] = [];
+    }
+
+    answer[lv].push(current.val);
+
+    if (current.left) {
+      q.push([current.left, lv + 1]);
+    }
+
+    if (current.right) {
+      q.push([current.right, lv + 1]);
+    }
+  }
+
+  return answer;
+};