feat: add mobius.cpp #14
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7-math/mobius.cpp
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| for (auto &p : prime) { | ||
| ll v = 1LL * p * i; | ||
| if (v > n) break; | ||
| lp[v] = p; | ||
| if (lp[i] = p) { mu[v] = 0; break; } | ||
| else mu[v] = -mu[i]; |
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The inner loop assigns lp[i] = p and immediately treats the branch as true. Because this is an assignment rather than a check on whether i is divisible by p, every iteration forces lp[i] to the current prime, mu[v] becomes 0, and the loop breaks. As a result, the function returns 0 for almost every value and never produces the correct ±1 Möbius values for square‑free integers. The conditional should test divisibility (i % p == 0) or compare against the least prime factor, instead of assigning.
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