Solved: 153. Find Minimum in Rotated Sorted Array #42
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fuga-98
reviewed
May 11, 2025
| while lo < hi: | ||
| mid = (lo + hi) // 2 | ||
| if nums[mid] <= nums[-1]: | ||
| hi = mid |
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ここ少し違和感ありました。
この問題の答えになる範囲は0からlen-1で、
137行目でhiをlenにしているので、hiは答えにならない最大のindexだと予想しました。
ただここでhi=midとすると、答えになりうる最大のindexに意味が変わってしまっているように思いました。
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私はloとhiはずっと同じ意味であってほしいと思いましたが、一般的なのかどうかはわからないです。
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これは、考え方次第で、「条件を満たす一番左の x を探す」という文脈では、条件を満たすものがないときに、len(nums) が返ってくるコードを書くのがよくあります。
ただ、今回は条件が nums[x] <= nums[-1] なので、必ず一番右端は条件を満たしますね。
fuga-98
reviewed
May 11, 2025
| hi = mid - 1 | ||
| else: | ||
| lo = mid + 1 | ||
|
|
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メモ
[5613]でやってみます
lo hi mid
0 3 2
0 1 1
2 1 ループ終了
面白い動きをするなとおもいました。
おそらくmidの切り上げで動くソースを書いたのだと思いますが、探索範囲に答えがない二分探索も書けるんですね。
Owner
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ご指摘ありがとうございます。
ここ、探索範囲が狭まるだろうくらいの認識で、きちんとシミュレーションできていませんでした。
切り下げ/切り上げの選択は自信を持って説明できないので、もう少し考えてみます。
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153. Find Minimum in Rotated Sorted Array