牛客网暑期ACM多校训练营(第一场) A.Monotonic Matrix (不相交路径Lindström–Gessel–Viennot lemma定理+组合数)
题目链接时间限制:C/C++1秒,其他语言2秒空间限制:C/C++524288K,其他语言1048576K64bitIOFormat:%lld题目描述CountthenumberofnxmmatricesAsatisfyingthefollowingconditionmodulo(109+7).*Ai,j∈{0,1,2}forall1≤i≤n,1≤j≤m.*Ai,j≤Ai+1,jforall1≤i