class SumInLeavesVisitor extends TreeVis { private int sum = 0;

public int getResult() {
    return sum;
}

public void visitNode(TreeNode node) {
    // Do nothing for non-leaf nodes
}

public void visitLeaf(TreeLeaf leaf) {
    sum += leaf.getValue();
}

}

class ProductOfRedNodesVisitor extends TreeVis { private long product = 1; private final int MOD = 1000000007;

public int getResult() {
    return (int) (product % MOD);
}

public void visitNode(TreeNode node) {
    if (node.getColor() == Color.RED) {
        product = (product * node.getValue()) % MOD;
    }
}

public void visitLeaf(TreeLeaf leaf) {
    if (leaf.getColor() == Color.RED) {
        product = (product * leaf.getValue()) % MOD;
    }
}

}

class FancyVisitor extends TreeVis { private int sumNonLeafEvenDepth = 0; private int sumGreenLeaves = 0;

public int getResult() {
    return Math.abs(sumNonLeafEvenDepth - sumGreenLeaves);
}

public void visitNode(TreeNode node) {
    if (node.getDepth() % 2 == 0) {
        sumNonLeafEvenDepth += node.getValue();
    }
}

public void visitLeaf(TreeLeaf leaf) {
    if (leaf.getColor() == Color.GREEN) {
        sumGreenLeaves += leaf.getValue();
    }
}

}

public class Solution { private static int[] values; private static Color[] colors; private static Map> edges = new HashMap<>();

public static Tree solve() {
    Scanner scanner = new Scanner(System.in);
    int n = scanner.nextInt();

    values = new int[n];
    colors = new Color[n];

    for (int i = 0; i < n; i++) {
        values[i] = scanner.nextInt();
    }

    for (int i = 0; i < n; i++) {
        colors[i] = (scanner.nextInt() == 0) ? Color.RED : Color.GREEN;
    }

    for (int i = 0; i < n - 1; i++) {
        int u = scanner.nextInt() - 1;
        int v = scanner.nextInt() - 1;

        if (!edges.containsKey(u)) {
            edges.put(u, new HashSet<Integer>());
        }
        edges.get(u).add(v);

        if (!edges.containsKey(v)) {
            edges.put(v, new HashSet<Integer>());
        }
        edges.get(v).add(u);
    }
    scanner.close();

    return buildTree(0, 0);
}

private static Tree buildTree(int nodeIndex, int depth) {
    Set<Integer> neighbors = edges.get(nodeIndex);

    if (neighbors.isEmpty()) {
        return new TreeLeaf(values[nodeIndex], colors[nodeIndex], depth);
    }

    TreeNode node = new TreeNode(values[nodeIndex], colors[nodeIndex], depth);

    for (int neighbor : neighbors) {
        edges.get(neighbor).remove(nodeIndex);
        node.addChild(buildTree(neighbor, depth + 1));
    }

    return node;
}

class SumInLeavesVisitor extends TreeVis { private int sum = 0;

public int getResult() {
    return sum;
}

public void visitNode(TreeNode node) {
    // No action needed for internal nodes in this visitor
}

public void visitLeaf(TreeLeaf leaf) {
    sum += leaf.getValue();
}

}

class ProductOfRedNodesVisitor extends TreeVis { private double product = 1;

public int getResult() {
    return (int) product;
}

public void visitNode(TreeNode node) {
    increaseProduct(node);
}

public void visitLeaf(TreeLeaf leaf) {
    increaseProduct(leaf);
}

private void increaseProduct(Tree tree) {
    if (tree.getColor() == Color.RED) {
        product = (product * tree.getValue()) % (Math.pow(10, 9) + 7);
    }
}

}

class FancyVisitor extends TreeVis { private int nonLeafNodeSum = 0; private int greenLeafSum = 0;

public int getResult() {
    return Math.abs(nonLeafNodeSum - greenLeafSum);
}

public void visitNode(TreeNode node) {
    if (node.getDepth() % 2 == 0) {
        nonLeafNodeSum += node.getValue();
    }
}

public void visitLeaf(TreeLeaf leaf) {
    if (leaf.getColor() == Color.GREEN) {
        greenLeafSum += leaf.getValue();
    }
}

}

public class Solution {

public static Tree solve() {
    Scanner scan = new Scanner(System.in);
    int n = Integer.parseInt(scan.nextLine());
    String valuesLine = scan.nextLine();
    String colorsLine = scan.nextLine();

    String[] valuesStr = valuesLine.split(" ");
    int[] values = new int[n];

    for (int i = 0; i < n; i++) {
        values[i] = Integer.parseInt(valuesStr[i]);
    }

    String[] colorsStr = colorsLine.split(" ");
    byte[] colors = new byte[n];

    for (int i = 0; i < n; i++) {
        colors[i] = (byte) Integer.parseInt(colorsStr[i]);
    }

    Map<Integer, List<Integer>> adj = new HashMap<>();
    boolean[] visited = new boolean[n];

    for (int i = 0; i < n; i++) {
        adj.put(i, new ArrayList<Integer>());
    }

    while (scan.hasNextInt()) {
        int u = scan.nextInt() - 1;
        int v = scan.nextInt() - 1;
        adj.get(u).add(v);
        adj.get(v).add(u);
    }

    scan.close();

    return buildTree(0, 0, values, colors, adj, visited);
}

public static Tree buildTree(
    int index, int depth, int[] values, byte[] colors, Map<Integer, List<Integer>> adj, boolean[] visited
) {
    boolean isLeaf = true;
    visited[index] = true;

    Color color = colors[index] == 0 ? Color.RED : Color.GREEN;
    List<Integer> children = adj.get(index);
    TreeNode treeNode = new TreeNode(values[index], color, depth);

    for (int child : children) {
        if (!visited[child]) {
            isLeaf = false;
            Tree childNode = buildTree(child, depth + 1, values, colors, adj, visited);
            treeNode.addChild(childNode);
        }
    }

    if (isLeaf) {
        return new TreeLeaf(values[index], color, depth);
    } else {
        return treeNode;
    }
}

what?!?

java solution with the supposed pre-existing classes

public class Solution {
    static int n;
    static int[] values;
    static Color[] colors;
    static Map<Integer, Set<Integer>> edges;

    public static void main(String[] args) {
        Tree root = solve();

        SumInLeavesVisitor vis1 = new SumInLeavesVisitor();
        ProductRedNodesVisitor vis2 = new ProductRedNodesVisitor();
        FancyVisitor vis3 = new FancyVisitor();

        root.accept(vis1);
        root.accept(vis2);
        root.accept(vis3);

        System.out.println(vis1.getResult());
        System.out.println(vis2.getResult());
        System.out.println(vis3.getResult());
    }
    
     public static Tree solve() {
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();

        values = new int[n+1];
        for (int i = 1; i <= n; i++) {
            values[i] = sc.nextInt();
        }

        colors = new Color[n+1];
        for (int i = 1; i <= n; i++) {
            int c = sc.nextInt();
            colors[i] = (c == 0 ? Color.RED : Color.GREEN);
        }

        edges = new HashMap<>();
        for (int i = 1; i <= n; i++) edges.put(i, new HashSet<>());
        for (int i = 0; i < n-1; i++) {
            int u = sc.nextInt();
            int v = sc.nextInt();
            edges.get(u).add(v);
            edges.get(v).add(u);
        }

        sc.close();
        return buildTree(1, 0, -1); // root=1, depth=0, parent=-1
    }    
    
    private static Tree buildTree(int node, int depth, int parent) {
        Set<Integer> childs = edges.get(node);
        if(childs.size() == 1 && childs.contains(parent)){
            //es hoja
            return new TreeLeaf(values[node], colors[node], depth);
        } else {
            TreeNode tn = new TreeNode(values[node], colors[node], depth);
            for(int child : childs){
                if(child != parent) {
                    tn.addChild(buildTree(child, depth+1, node));
                }
            }
            return tn;
        }
    }
}

enum Color {RED, GREEN}

abstract class Tree {
    private int value;
    private Color color;
    private int depth;
    
    public Tree(int value, Color color, int depth){
        this.value = value;
        this.color = color;
        this.depth = depth;
        
    }
    
    public int getValue(){ return value;}
    public Color getColor(){ return color;}
    public int getDepth(){ return depth;}
    
    public abstract void accept(TreeVis visitor);
}

class TreeNode extends Tree{
    private List<Tree> children = new ArrayList<>();
    
    public TreeNode(int value, Color color, int depth){
        super(value, color, depth);
    }
    
    public void accept(TreeVis visitor){
        visitor.visitNode(this);
        for(Tree child : children){
            child.accept(visitor);
        }
    }
    
    public void addChild(Tree child){ children.add(child); }
}

class TreeLeaf extends Tree{
    public TreeLeaf(int value, Color color, int depth){
        super(value, color, depth);
    }
    
    public void accept(TreeVis visitor){
        visitor.visitLeaf(this);
    }
}

interface TreeVis{
    int getResult();
    void visitNode(TreeNode tree);
    void visitLeaf(TreeLeaf tree);
}

class SumInLeavesVisitor implements TreeVis {
    private int sum = 0;
    
    public int getResult(){ return sum; }
    
    public void visitNode(TreeNode node){ /*no hace nada*/ }
    
    public void visitLeaf(TreeLeaf leaf){
        sum += leaf.getValue();
    }
}

class ProductRedNodesVisitor implements TreeVis {
    private long product = 1;
    private static final int MOD = 1000000007;
     
    public int getResult(){ return (int)(product % MOD); }
    
    public void visitNode(TreeNode node){ 
        if(node.getColor() == Color.RED)
            product = (product * node.getValue()) % MOD;
     }
    
    public void visitLeaf(TreeLeaf leaf) {
        if (leaf.getColor() == Color.RED) {
            product = (product * leaf.getValue()) % MOD;
        }
    }
}

class FancyVisitor  implements TreeVis {
    private int evenDepthNonLeafSum  = 0;
    private int greenLeafSum = 0;
     
    public int getResult(){ return (int)(Math.abs( evenDepthNonLeafSum - greenLeafSum)); }
    
    public void visitNode(TreeNode node){ 
        if(node.getDepth()  % 2 == 0)
            evenDepthNonLeafSum += node.getValue();
     }
    
    public void visitLeaf(TreeLeaf leaf) {
        if (leaf.getColor() == Color.GREEN) {
            greenLeafSum += leaf.getValue();
        }
    }
}

I don't get it are this clases provided? or do we have to implement them? abstract class Tree class TreeNode extends Tree class TreeLeaf extends Tree abstract class TreeVis

because the compiler is not able to find the but the text says: "A Tree class implementing a rooted tree is provided in the editor"