Codeforces Round #763 (Div. 2) D.Robot Cleaner Revisit 期望/思维
|——>传送门#defineintlonglong#defineendl'\n'usingnamespacestd;constintN=2e5+10,MOD=1e9+7;inta[N],b[N];inlineintbinpow(intx,inty,intmod,intres=1){for(;y;y>>=1,(x*=x)%=mod)if(y&1)(res*=x)%=mod;returnres;}in