AtCoder Beginner Contest 327 G. Many Good Tuple Problems(带标号二分图计数+有区别小球放入有区别盒子)
题目一个长为n(nusingnamespacestd;#definerep(i,a,b)for(inti=(a);i=(b);--i)typedeflonglongll;typedefdoubledb;typedefpairP;#definefifirst#definesesecond#definepbpush_back#definedbg(x)cerr>=1,x=1ll*x*x%mod){if(