Java Program for Range sum queries without updates

Given an array arr of integers of size n. We need to compute sum of elements from index i to index j. The queries consisting of i and j index values will be executed multiple times. Examples:

Input : arr[] = {1, 2, 3, 4, 5}
        i = 1, j = 3
        i = 2, j = 4
Output :  9
         12         

Input : arr[] = {1, 2, 3, 4, 5}
        i = 0, j = 4 
        i = 1, j = 2 
Output : 15
          5

Java

// Java program to find sum between two indexes
// when there is no update.

import java.util.*;
import java.lang.*;

class GFG {
 public static void preCompute(int arr[], int n, int pre[])
 {
  pre[0] = arr[0];
  for (int i = 1; i < n; i++)
   pre[i] = arr[i] + pre[i - 1];
 }

 // Returns sum of elements in arr[i..j]
 // It is assumed that i <= j
 public static int rangeSum(int i, int j, int pre[])
 {
  if (i == 0)
   return pre[j];

  return pre[j] - pre[i - 1];
 }

 public static void main(String[] args)
 {
  int arr[] = { 1, 2, 3, 4, 5 };
  int n = arr.length;

  int pre[] = new int[n];

  preCompute(arr, n, pre);
  System.out.println(rangeSum(1, 3, pre));
  System.out.println(rangeSum(2, 4, pre));
 }
}

// Code Contributed by Mohit Gupta_OMG <(0_o)>

Output:

9
12

Time Complexity: O(n), where n represents the size of the given array.
Auxiliary Space: O(n), where n represents the size of the given array.

Please refer complete article on Range sum queries without updates for more details!