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 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

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

My Personal Notes

Suggest a Topic

Recommended Posts: