binary-tree-level-order-traversal solution (ts)

Author: hi-rachel

binary-tree-level-order-traversal/hi-rachel.ts

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+/**
+ * python의 len(queue)는 반복 시작 전에 계산된 값, 즉 고정된 횟수만큼 반복
+ * JS의 queue.length는 반복마다 실시간으로 다시 계산하므로 고정 사이즈 size 변수 사용
+ */
+
+/**
+ * Definition for a binary tree node.
+ */
+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;
+  }
+}
+
+function levelOrder(root: TreeNode | null): number[][] {
+  if (!root) return [];
+
+  const queue: TreeNode[] = [root];
+  const output: number[][] = [];
+
+  while (queue.length > 0) {
+    const level: number[] = [];
+    for (let node of queue) {
+      level.push(node.val);
+    }
+    output.push(level);
+    const size = queue.length;
+
+    for (let i = 0; i < size; i++) {
+      const node = queue.shift();
+      if (node && node.left) {
+        queue.push(node.left);
+      }
+      if (node && node.right) {
+        queue.push(node.right);
+      }
+    }
+  }
+  return output;
+}