2023 Hunan Provincal Multi-University Training (Xiangtan University) B. 阶梯计数(第二类斯特林数)
题目题目链接:Problem-B-CodeforcesImakf送给了Clamee一个n行n列(nusingnamespacestd;#definerep(i,a,b)for(inti=(a);i=(b);--i)typedeflonglongll;typedefdoubledb;typedefpairP;#definefifirst#definesesecond#definepbpush_bac