ICPC Pacific Northwest Regional Contest 2019 ABCDEM
A:经典的换根dp拆成维护两个求和符号里的值。换根即可。#includeusingnamespacestd;typedeflonglongll;constintM=1e5+7;inthead[M],cnt;structEDGE{intto,nxt,val;}ee[M*2];voidadd(intx,inty,intw){ee[++cnt].nxt=head[x],ee[cnt].to=y,ee[c