Add binary-tree-level-order-traversal solution in TS

Author: Jeehay28

binary-tree-level-order-traversal/Jeehay28.ts

@@ -0,0 +1,42 @@
+ class TreeNode {
+     val: number
+     left: TreeNode | null
+     right: TreeNode | null
+     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+         this.val = (val===undefined ? 0 : val)
+         this.left = (left===undefined ? null : left)
+         this.right = (right===undefined ? null : right)
+     }
+ }
+
+
+// TC: O(n)
+// SC: O(n)
+function levelOrder(root: TreeNode | null): number[][] {
+  if (!root) return [];
+
+  const result: number[][] = [];
+  const queue: TreeNode[] = [root];
+
+  while (queue.length > 0) {
+    const values: number[] = [];
+    const level = queue.length;
+
+    for (let i = 0; i < level; i++) {
+      const node = queue.shift()!;
+      values.push(node.val);
+
+      if (node.left) {
+        queue.push(node.left);
+      }
+
+      if (node.right) {
+        queue.push(node.right);
+      }
+    }
+
+    result.push(values);
+  }
+
+  return result;
+}