ABC121D
考えたこと
各ビットごとに考えると、2べきの剰余で区間内の1の数がわかるよね
公式解説
それは対数オーダー解
下記に気づくと定数オーダー
f(A, B) = f(0, A - 1) \oplus f(0, B)
2n \oplus (2n+1) = 1
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