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Optimize and make Modint safer #318

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Merged
simonlindholm merged 1 commit into from
Jun 23, 2026
Merged

Optimize and make Modint safer #318

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15 changes: 8 additions & 7 deletions content/number-theory/ModularArithmetic.h
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/**
* Author: Lukas Polacek
* Author: Lukas Polacek, Joshua Andersson
* Date: 2009-09-28
* License: CC0
* Source: folklore
Expand All @@ -13,17 +13,18 @@
const ll mod = 17; // change to something else
struct Mod {
ll x;
Mod(ll xx) : x(xx) {}
Mod operator+(Mod b) { return Mod((x + b.x) % mod); }
Mod operator-(Mod b) { return Mod((x - b.x + mod) % mod); }
Mod operator*(Mod b) { return Mod((x * b.x) % mod); }
Mod(ll y) : Mod(y%mod+mod,0){}
Mod(ll y,int) : x(y<mod?y:y-mod){}
Mod operator+(Mod b) { return {x + b.x,0}; }
Mod operator-(Mod b) { return {x - b.x + mod,0}; }
Mod operator*(Mod b) { return {x * b.x % mod,0}; }
Mod operator/(Mod b) { return *this * invert(b); }
Mod invert(Mod a) {
ll x, y, g = euclid(a.x, mod, x, y);
assert(g == 1); return Mod((x + mod) % mod);
assert(g == 1); return x;
}
Mod operator^(ll e) {
if (!e) return Mod(1);
if (!e) return 1;
Mod r = *this ^ (e / 2); r = r * r;
return e&1 ? *this * r : r;
}
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