HackerEarth Minimize the value problem solution

In this HackerEarth Minimize the value problem solution You are given a binary tree rooted at 1. Initially, all the nodes of the tree have some initial values Vi. Wave operation is to be applied on the tree.

After applying the wave operation,

Value of each node in the tree = Sum of all initial values of nodes in its subtree.

You are required to add 1 more node with value X to the tree such that:

1. The tree remains binary after adding the node to the tree.
2. After applying the wave operation to this tree (the tree after adding node with value X), the sum of tree is minimum.

Sum of tree = sum of values of all nodes in the tree.

Print the minimum sum of the tree.

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.FilterInputStream;
import java.io.BufferedInputStream;
import java.util.LinkedList;
import java.util.ArrayList;
import java.io.InputStream;

public class Main {
    public static void main(String[] args) {
        new Thread(null, new Runnable() {
            public void run() {
                new Main().solve();
            }
        }, "1", 1 << 26).start();
    }

    void solve() {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        ScanReader in = new ScanReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Minimisethemagic solver = new Minimisethemagic();
        solver.solve(1, in, out);
        out.close();
    }

    static class Minimisethemagic {
        private ArrayList<Integer>[] arrayList;
        private int[] array;
        private long[] ans_ar;

        private int bfs(int node) {
            LinkedList<Integer> linkedList = new LinkedList<>();
            linkedList.add(1);
            while (linkedList.size() != 0) {
                int temp = linkedList.remove(0);
                if (temp == 1) {
                    if (arrayList[1].size() < 2) return 1;
                    if (arrayList[1].size() > 2) throw new RuntimeException();
                } else {
                    if (arrayList[temp].size() < 3) return temp;
                    if (arrayList[temp].size() > 3) throw new RuntimeException();
                }

                for (int i = 0; i < arrayList[temp].size(); i++) {
                    linkedList.add(arrayList[temp].get(i));
                }
            }
            return -1;
        }

        private long findIt(int node, int p) {
            long temp = array[node];
            for (int i = 0; i < arrayList[node].size(); i++) {
                if (arrayList[node].get(i) == p) continue;
                temp += findIt(arrayList[node].get(i), node);
            }
            return ans_ar[node] = temp;
        }

        public void solve(int testNumber, ScanReader in, PrintWriter out) {
            int n = in.scanInt();
            if (n < 1 || n > 100000) throw new RuntimeException();
            int value = in.scanInt();
            if (value < 1 || value > 1000000000) throw new RuntimeException();
            array = new int[n + 2];
            arrayList = new ArrayList[n + 2];
            ans_ar = new long[n + 2];
            for (int i = 0; i <= n + 1; i++) arrayList[i] = new ArrayList<>();
            for (int i = 1; i <= n; i++)
                if ((array[i] = in.scanInt()) < 1 || array[i] > 1000000000) throw new RuntimeException();
            array[n + 1] = value;
            for (int i = 0; i < n - 1; i++) {
                int x = in.scanInt();
                int y = in.scanInt();
                arrayList[x].add(y);
                arrayList[y].add(x);
            }
            int node = bfs(1);
            if (node == -1) throw new RuntimeException("Really ? ");
            arrayList[node].add(n + 1);
            findIt(1, -1);
            long ans = 0;
            for (int i = 0; i <= n + 1; i++) ans += ans_ar[i];
            out.println(ans);
        }

    }

    static class ScanReader {
        private byte[] buf = new byte[4 * 1024];
        private int index;
        private BufferedInputStream in;
        private int total;

        public ScanReader(InputStream inputStream) {
            in = new BufferedInputStream(inputStream);
        }

        private int scan() {
            if (index >= total) {
                index = 0;
                try {
                    total = in.read(buf);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                if (total <= 0) return -1;
            }
            return buf[index++];
        }

        public int scanInt() {
            int integer = 0;
            int n = scan();
            while (isWhiteSpace(n)) n = scan();
            int neg = 1;
            if (n == '-') {
                neg = -1;
                n = scan();
            }
            while (!isWhiteSpace(n)) {
                if (n >= '0' && n <= '9') {
                    integer *= 10;
                    integer += n - '0';
                    n = scan();
                }
            }
            return neg * integer;
        }

        private boolean isWhiteSpace(int n) {
            if (n == ' ' || n == 'n' || n == 'r' || n == 't' || n == -1) return true;
            else return false;
        }

    }
}