Queries for the count of even digit sum elements in the given range using Segment Tree.

// Java implementation of the approach
import java.util.*;
class GFG{

// Function to find the digit sum
// for a number
static int digitSum(int num)
{
    int sum = 0;
    while (num > 0) 
    {
        sum += (num % 10);
        num /= 10;
    }
    return sum;
}

// Procedure to build the segment tree
static void buildTree(int []tree, int []arr,
                int index, int s, int e)
{

    // Reached the leaf node
    // of the segment tree
    if (s == e) 
    {
        if (digitSum(arr[s]) % 2 == 1)
            tree[index] = 0;
        else
            tree[index] = 1;
        return;
    }

    // Recursively call the buildTree
    // on both the nodes of the tree
    int mid = (s + e) / 2;
    buildTree(tree, arr, 2 * index,
              s, mid);
    buildTree(tree, arr, 2 * index + 1,
              mid + 1, e);

    tree[index] = tree[2 * index] + 
                    tree[2 * index + 1];
}

// Query procedure to get the answer
// for each query l and r are
// query range
static int query(int []tree, int index, 
                 int s, int e, 
                 int l, int r)
{

    // Out of bound or no overlap
    if (r < s || l > e)
        return 0;

    // Complete overlap
    // Query range completely lies in
    // the segment tree node range
    if (s >= l && e <= r)
    {
        return tree[index];
    }

    // Partially overlap
    // Query range partially lies in
    // the segment tree node range
    int mid = (s + e) / 2;
    return (query(tree, 2 * index, s,
                  mid, l, r) +
            query(tree, 2 * index + 1, 
                  mid + 1, e, l, r));
}

// Driver code
public static void main(String[] args)
{
    int arr[] = { 7, 3, 19, 13, 5, 4 };
    int n = arr.length;
    int []tree = new int[4 * n + 1];

    int L = 1, R = 5;

    buildTree(tree, arr, 1, 0, n - 1);

    System.out.print(query(tree, 1, 0, 
                           n - 1, L, R) + "\n");
}
}

// This code is contributed by gauravrajput1 

// Added by: Nikunj Sonigara

import java.util.*;

public class Main {
    static int getDigitSum(int num) {
        // Returns the digit sum of the given number
        int digitSum = 0;
        while (num > 0) {
            digitSum += num % 10;
            num /= 10;
        }
        return digitSum;
    }

    static int countEvenDigitSum(List<Integer> arr, int left, int right) {
        // Counts the number of elements with even digit sum in the subarray [left, right]
        int count = 0;
        for (int i = left; i <= right; i++) {
            if (getDigitSum(arr.get(i)) % 2 == 0) {
                count++;
            }
        }
        return count;
    }

    static List<Integer> countEvenDigitSumQueries(List<Integer> arr, List<Pair<Integer, Integer>> queries) {
        // Counts the number of elements with even digit sum for each query
        List<Integer> results = new ArrayList<>();
        for (Pair<Integer, Integer> query : queries) {
            int left = query.getKey();
            int right = query.getValue();
            results.add(countEvenDigitSum(arr, left, right));
        }
        return results;
    }

    public static void main(String[] args) {
        List<Integer> arr = List.of(7, 3, 19, 13, 5, 4);
        List<Pair<Integer, Integer>> queries = List.of(new Pair<>(1, 5));

        List<Integer> results = countEvenDigitSumQueries(arr, queries);

        System.out.print("[");
        for (int i = 0; i < results.size(); i++) {
            System.out.print(results.get(i));
            if (i < results.size() - 1) {
                System.out.print(", ");
            }
        }
        System.out.println("]");

        arr = List.of(0, 1, 2, 3, 4, 5, 6, 7);
        queries = List.of(new Pair<>(3, 5));

        results = countEvenDigitSumQueries(arr, queries);

        System.out.print("[");
        for (int i = 0; i < results.size(); i++) {
            System.out.print(results.get(i));
            if (i < results.size() - 1) {
                System.out.print(", ");
            }
        }
        System.out.println("]");
    }
}

class Pair<K, V> {
    private final K key;
    private final V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() {
        return key;
    }

    public V getValue() {
        return value;
    }
}