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Same Tree #45
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Same Tree #45
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,29 @@ | ||
//lint:file-ignore U1000 Ignore all unused code | ||
package sametree | ||
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type TreeNode struct { | ||
Val int | ||
Left *TreeNode | ||
Right *TreeNode | ||
} | ||
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/* | ||
レビュワーの方へ: | ||
- このコードは既にGoの標準のフォーマッタで整形済みです。演算子の周りにスペースがあったりなかったりしますが、これはGoのフォーマッタによるもので、優先順位の高い演算子の周りにはスペースが入らず、低い演算子の周りには入るようになっています。https://qiita.com/tchssk/items/77030b4271cd192d0347 | ||
*/ | ||
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/* | ||
時間:3分30秒 | ||
*/ | ||
func isSameTreeStep1(p *TreeNode, q *TreeNode) bool { | ||
if p == nil && q == nil { | ||
return true | ||
} | ||
if p == nil || q == nil { | ||
return false | ||
} | ||
if p.Val != q.Val { | ||
return false | ||
} | ||
return isSameTreeStep1(p.Left, q.Left) && isSameTreeStep1(p.Right, q.Right) | ||
} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,20 @@ | ||
//lint:file-ignore U1000 Ignore all unused code | ||
package sametree | ||
|
||
/* | ||
レビュワーの方へ: | ||
- このコードは既にGoの標準のフォーマッタで整形済みです。演算子の周りにスペースがあったりなかったりしますが、これはGoのフォーマッタによるもので、優先順位の高い演算子の周りにはスペースが入らず、低い演算子の周りには入るようになっています。https://qiita.com/tchssk/items/77030b4271cd192d0347 | ||
*/ | ||
|
||
/* | ||
リファクタした。 | ||
*/ | ||
func isSameTreeStep2(p *TreeNode, q *TreeNode) bool { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Iterative DFS/BFSでも書けますか? There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. 再帰をループに直すのは、練習としてわりと重要度高いと個人的には思っています。機会があれば、手の運動くらいの気持ちで。 |
||
if p == nil && q == nil { | ||
return true | ||
} | ||
if p == nil || q == nil || p.Val != q.Val { | ||
return false | ||
} | ||
return isSameTreeStep2(p.Left, q.Left) && isSameTreeStep2(p.Right, q.Right) | ||
} |
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ある木が木の集合中に存在するかを調べたいという問題だったらどうしますか?このクエリは複数回発行されるものとします。
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検索を効率化するために例えば下記のように木全体をハッシュ化するなどはいかがでしょうか。
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この問題とは関係ないですが、木の全ての部分木もハッシュ化したいならどうしますか?全ての部分木に対してpre-order traversalをするのは効率が悪そうです。
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post-orderで下から順に各ノードでハッシュを計算し、親ノードは左右子ノードのハッシュ値を使ってハッシュを計算するという形にするのが良さそうな気がしました。
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in-orderではないですか?
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すみません。post-orderですね。
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https://en.wikipedia.org/wiki/Merkle_tree
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ありがとうございます。全く考えてなかったことなので勉強になりました。
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Merkle treeというのがあるのですね、、