Created
April 13, 2019 07:06
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中国剩余定理
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// 要求:a>=0, b>=0 | |
void ext_gcd(ll a, ll b, ll &x, ll &y){ | |
// 迭代不变量: | |
// x*a + b*y == gcd(a,b); | |
if(b==0){ | |
x=1; | |
y=0; | |
return; | |
} | |
// ext_gcd(a, a%b, x, y) | |
// gcd(a,b) == x*a + y*(a-a/b*b) | |
// gcd(a,b) == (x+y)*a + (-a/b*y)b; | |
ext_gcd(b, a%b, y, x); | |
// x*(a-a/b*b) + b*y = gcd(a,b) | |
//x*a + (y-x*a/b)*b | |
y -= x*a/b; | |
} | |
ll inv(ll x, ll m){ | |
ll a, b; | |
ext_gcd(x, m, a, b); | |
a%=m; | |
if(a<0) a+=m; | |
return a; | |
} | |
// pair.first 余数, pair.second 模数 | |
ll crt(const vector<pair<ll,ll>> &a){ | |
ll prod = 1; | |
// 要求:所有模数之积不会溢出 | |
for(auto x: a) { | |
prod *= x.second; | |
} | |
ll res = 0; | |
for(auto x: a){ | |
auto t = prod/x.second; | |
res += x.first * t % prod * inv(t, x.second) % prod; // error-prone | |
if(res >= prod) res -= prod; | |
} | |
return res; | |
} |
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