Codeforces 960E Alternating Tree 树型DP

E. Alternating Tree

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Given a tree with $n$ nodes numbered from $1$ to $n$. Each node $i$ has an associated value $V_i$.

If the simple path from $u_1$ to $u_m$ consists of $m$ nodes namely $u_1\to u_2\to u_3\to \dots u_{m-1}\to u_m$, then its alternating function $A(u_1,u_m)$ is defined as $A(u_1,u_m)=\sum _{i=1}^m(-1{)}^{i+1}\cdot V_{u_i}$. A path can also have $0$edges, i.e. $u_1$