Help me in solving DSAAGP14 problem

help
,
1

My issue

test case fails , 100000

My code

#include <bits/stdc++.h>

using namespace std;

void solve_queries() {
    size_t N, K;
    cin >> N;
    vector < uint32_t > arr(N);
    for (int i = 0; i < N; i++)
    {
        cin >> arr[i];
    }

    vector < uint64_t > prefix_sum(N + 1, 0);
    for (int i = 1; i <= N; i++) {
        prefix_sum[i] = prefix_sum[i - 1] + arr[i - 1];
    }

    cin >> K;

    for (int i = 0; i < K; i++)
    {
        size_t a, b;
        cin >> a >> b;
        uint64_t result = prefix_sum[b] = prefix_sum[a - 1];
        cout << result << "\n";
    }
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    solve_queries();
    return 0;
}

Learning course: Data structures & Algorithms lab
Problem Link: https://www.codechef.com/learn/course/muj-aiml-dsa-c/MUJADSAC07/problems/DSAAGP14