20 lines
402 B
C++
20 lines
402 B
C++
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constexpr int N = 1e7 + 10;
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int lpf[N];
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void era(int n) {
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lpf[0] = lpf[1] = -1;
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for (int i = 2; i <= n; ++i) lpf[i] = i;
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for (int i = 2; i <= n; ++i) {
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if (lpf[i] == i) {
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if ((ll)i * i > n) continue;
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for (int j = i * i; j <= n; j += i) {
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if (lpf[j] == j) {
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lpf[j] = i;
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}
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}
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}
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}
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}
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