Feat: 102. Binary Tree Level Order Traversal

Author: HC-kang

binary-tree-level-order-traversal/HC-kang.ts

@@ -0,0 +1,57 @@
+// 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;
+//   }
+// }
+
+/**
+ * https://leetcode.com/problems/binary-tree-level-order-traversal
+ * T.C. O(n)
+ * S.C. O(n)
+ */
+function levelOrder(root: TreeNode | null): number[][] {
+  const result: number[][] = [];
+  function dfs(node: TreeNode | null, level: number) {
+    if (!node) return;
+    if (!result[level]) result[level] = [];
+    result[level].push(node.val);
+    dfs(node.left, level + 1);
+    dfs(node.right, level + 1);
+  }
+  dfs(root, 0);
+  return result;
+}
+
+/**
+ * bfs
+ * T.C. O(n)
+ * S.C. O(n)
+ */
+function levelOrder(root: TreeNode | null): number[][] {
+  const result: number[][] = [];
+  if (!root) return result;
+
+  const queue: TreeNode[] = [root];
+  let start = 0;
+
+  while (queue[start]) {
+    const levelSize = queue.length - start;
+    const currentLevel: number[] = [];
+
+    for (let i = 0; i < levelSize; i++) {
+      const node = queue[start++];
+      currentLevel.push(node.val);
+      if (node.left) queue.push(node.left);
+      if (node.right) queue.push(node.right);
+    }
+
+    result.push(currentLevel);
+  }
+
+  return result;
+}