牛客网暑期ACM多校训练营(第一场) A Monotonic Matrix(Lindström–Gessel–Viennot lemma)
Description:CountthenumberofnxmmatricesAsatisfyingthefollowingconditionmodulo(109+7).Ai,j∈{0,1,2}forall1≤i≤n,1≤j≤m.Ai,j≤Ai+1,jforall1≤iusingnamespacestd;#definemem(a,b)memset(a,b,sizeof(a))#definepbpu