*[hackerrank]Cut the tree

https://www.hackerrank.com/contests/w2/challenges/cut-the-tree

树分成两部分，求两部分差最小。一开始想多了，后来其实求一下总和，求一下分部的和就行了。

#include <cstdlib>
#include <climits>
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

vector<vector<int>> tree;
vector<bool> visited;
vector<int> val;
int totalVal;

int subSum(int root, int& minCut) {
	int sum = 0;
	visited[root] = true;
	for (int i = 0; i < tree[root].size(); i++) {
		int sub = tree[root][i];
		if (visited[sub])
			continue;
		int x = subSum(sub, minCut);
		sum += x;
	}
	sum += val[root];
    minCut = min(minCut, abs(totalVal - 2 * sum));
    return sum;
}
int main() {
	int N;
	cin >> N;
	tree.resize(N + 1);
	visited.resize(N + 1);
	val.resize(N + 1);
	totalVal = 0;
	for (int i = 1; i <= N; i++) {
		cin >> val[i];
		totalVal += val[i];
	}
	for (int i = 0; i < N - 1; i++) {
		int a, b;
		cin >> a >> b;
		tree[a].push_back(b);
		tree[b].push_back(a);
	}
	int minCut = INT_MAX;
	// pick 1 as root
	subSum(1, minCut);
	cout << minCut << endl;
	return 0;
}