using System;

using System.Collections.Generic;

​

public class Program

{

    private static int maxFreq;

    private static Dictionary<int, int> dict;

    public static void Main()

    {

        var tree = new Tree();

        tree.root = new Node(5);

        tree.root.left = new Node(2);

        tree.root.right = new Node(-5);

        var tree1 = new Tree();

        tree1.root = new Node(5);

        tree1.root.left = new Node(2);

        tree1.root.right = new Node(-3);

        var freqSub = Program.GetMostFrequentSubtreeSum(tree.root);

        foreach (var val in freqSub) {

            Console.WriteLine(val);

        }

        var freqSub1 = Program.GetMostFrequentSubtreeSum(tree1.root);

        foreach (var val in freqSub1) {

            Console.WriteLine(val);

        }

    }

    public static List<int> GetMostFrequentSubtreeSum(Node root) {

        maxFreq = 0;

        dict = new Dictionary<int, int>();

        IterateTree(root, dict);

        var keyList = new List<int>(dict.Keys);

        var resultList = new List<int>();

        foreach (int key in keyList) {

            if (maxFreq == dict[key]) {

                resultList.Add(key);

            }

        }

        return resultList;

    }

    public static int IterateTree(Node node, Dictionary<int, int> dict) {

        if (node == null) return 0;

        var sum = IterateTree(node.left, dict) + IterateTree(node.right, dict) + node.value;

        var curFreq = dict.ContainsKey(sum) ? dict[sum] : 0;

        curFreq++;

        dict[sum] = curFreq;

        if (curFreq > maxFreq) {

            maxFreq = curFreq;

        }

        return sum;

    }

}

​

public class Node {

    public int value;

    public Node left, right;

    public Node(int val) {

        value = val;

    }

}

​

public class Tree {

    public Node root;

    public Tree() { 

        root = null; 

    }

}

​