Fast Range Sum
Submit solution
Points:
100
Time limit:
1.0s
Memory limit:
256M
Author:
Problem type
Allowed languages
C, C++
You are given an integer sequence \(a_1, a_2, \ldots, a_N\) of length \(N\). There are \(Q\) queries; the \(i\)-th query specifies \(L_i\) and \(R_i\), and you must output \(\sum_{j=L_i}^{R_i} a_j\), the sum of the elements between indices \(L_i\) and \(R_i\) inclusive.
Input
The first line contains two integers \(N\) and \(Q\).
The second line contains \(N\) integers \(a_1, a_2, \ldots, a_N\).
Each of the next \(Q\) lines contains two integers \(L_i\) and \(R_i\).
Constraints
- \(1 \le N, Q \le 2 \times 10^5\)
- \(1 \le a_i \le 10^4\)
- \(1 \le L_i \le R_i \le N\)
Output
For each query, print one integer on its own line: the sum over that range.
Scoring
There are three subtasks. Each subtask contains multiple test cases, and you earn the subtask's score only if you solve all of its tests.
- Subtask \(1\) (20 points): \(N, Q \le 5000\).
- Subtask \(2\) (40 points): \(L_i = 1\).
- Subtask \(3\) (40 points): no additional constraints.
Sample Input 1
5 3
1 2 3 4 5
1 3
2 5
4 4
Sample Output 1
6
14
4