31. Next Permutation #50
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potrue
reviewed
Oct 11, 2025
| end | ||
| nil | ||
| end | ||
| rfind_first_greater_than = lambda do |target| |
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一応ここは二分探索が使えますね。(pivot_indexの一つ右からnumsの最後までは降順にソートされているので)
potrue
reviewed
Oct 11, 2025
| right -= 1 | ||
| end | ||
| end | ||
| rfind_first_ascending = lambda do |
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右から見ていったときにはascendingではなくdescendingなのでちょっとややこしい気がします。(firstという単語のニュアンスでは右から見ている感じなので)
参考までに、c++ではis_sorted_untilという関数があったりします。そこから名前を取って、rfind_is_sorted_untilとかでもいいかもしれません。
あと、個人的にはnums.size - 1から初めてnums[i]とnums[i-1]の比較をしたいかもしれません。
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コメントありがとうございます！
is_sorted_until良いですね。
tokuhirat
reviewed
Oct 13, 2025
| nums.reverse! | ||
| return | ||
| end | ||
| swap_index = rfind_first_greater_than.call(nums[pivot_index]) |
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rfind_first_greater_than を使わずに以下のようにも書けると思いました。
swap_index = nums.rindex { |num| num > nums[pivot_index] }http://docs.ruby-lang.org/ja/latest/class/Array.html#I_RINDEX
折に触れてドキュメントを見ると発見があるかもしれません。
tokuhirat
reviewed
Oct 13, 2025
| nums[pivot_index], nums[swap_index] = nums[swap_index], nums[pivot_index] | ||
| reverse.call(pivot_index + 1, nums.size - 1) | ||
| end | ||
| ``` |
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lambda の定義の間には1行空行があった方が読みやすいと感じました。
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解いた問題
31. Next Permutation
使用言語
Ruby
次に解く問題
8. String to Integer (atoi)