102 binary tree level order traversal - #26
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miyataka
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Jul 18, 2026
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| ノード数 n に対して時間計算量 O(n)、空間計算量 O(n) | ||
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| ノード数の上限は 2000 であり各ノードについて val の取得、子の None 判定とリストへの append などを行う程度なので、計算回数は `2000 * 10 = 2 * 10 ^ 4`くらい、計算時間は 数十 ms くらいか。 |
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| - 「計算量 Time: O(V + E) = O(V), Space: O(width) = O(V)」 | ||
| - 自分では全部のノードを見るから O(V)、と雑に考えていたが、実際には高さの回数ループが回り、その中で同じ高さのノードの数だけループが回るという構造であることに気をつける必要がある |
| return [] | ||
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| nodes: list[TreeNode] = [root] | ||
| traversal: list[list[int]] = [] |
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traversal という変数名はすでに言及されている通り，すこし違和感がありましたが，後続で改善されていますね
skypenguins
reviewed
Jul 20, 2026
| if root is None: | ||
| return [] | ||
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| nodes = [root] |
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自分なら命名として nodes は pending_nodes とかにします。
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ありがとうございます。どういうノードかを明確に表現するのもわかりやすいですね。
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この問題：https://leetcode.com/problems/binary-tree-level-order-traversal/
次の問題：https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/