*[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;

}