计算n阶行列式的模板

function det(a:arr):int64;
var i,j,k:longint;
    t,ans:int64;

begin
    ans:=1;
    for i:=1 to n do
    begin
        for j:=i+1 to n do
        while a[j,i]<>0 do
        begin
            t:=a[i,i] div a[j,i];
            for k:=i to n do a[i,k]:=(a[i,k]-t*a[j,k]) mod p;
            for k:=1 to n do swap(a[i,k],a[j,k]);
            ans:=-ans;
        end;
        if a[i,i] = 0 then exit(0);
        ans:=(ans * a[i,i]) mod p;
    end;
    while ans<0 do inc(ans,p);
    exit(ans);
end;