range queries and one graph

CSES - CSES Problem Set/Range_Queries/Static_Range_Sum_Queries.cpp

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+//  Static Range Sum Queries
+
+#include<bits/stdc++.h>
+
+using namespace std;
+using ll = long long;
+
+int main() {
+    int n, q; cin >> n >> q;
+    vector<ll> pref(n, 0);
+    ll x; cin >> x;
+    pref[0] = x;
+    for (int i = 1; i < n; i ++) {
+        ll y; cin >> y;
+        pref[i] = y + pref[i-1];
+    }
+    for (int i{}; i < q; i++) {
+        int a, b; cin >> a >> b;
+        if (a >= 2 ) cout << pref[b - 1] - pref[a - 2] << endl;
+        else cout << pref[b - 1] << endl;
+    }
+
+    return 0;
+}