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
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// 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)>

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Output:



9
12

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



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