So currently, i was doing this problem that say

Given an array,you have to divide this array in to 2 bag,each element belong to 1 bag,find a way to do that the difference of the sum of these 2 bag is minimum.

I had made the observation that the result will not be greater than Max(a[i]),and did some dp and have passed. But i wasn't so sure that my observation is right or i just passed because of luck.

So i want to ask if it right or not.

Given a tree with N nodes, node i-th has c[i] (let say it mean node i-th cost), find P (P is given) node that are connected, and the sum of P node's cost is minimum N<=100000 P<=N C[i]<=100000 output sum of P node's cost (i don't speak english so sorry if it bad)

Given a tree with n node, a number P, every node i has a c[i], print the minimum-sum of P node that are connected Help me with this problems.

Can someone explain IOI 2011 RACE solution using CD?