Python Program for Range sum queries without updates

Given an array arr of integers of size n. We need to compute the 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

Method 1:

Python3

# Python program to find sum between two indexes
# when there is no update.

def find_ans(ar, j, k):
    l = len(ar)
    for i in range(1, l):
        ar[i] = ar[i] + ar[i-1]

    print(ar[k] - ar[j-1])
    return;


pr = [1, 2, 3, 4, 5]
ar = pr[:]
find_ans(ar, 1, 3)
ar = pr[:]
find_ans(ar, 2, 4)

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!

Method 2:

List splicing may be used, along with sum function, for a one-line approach to this problem.

Python3

# Python program to find sum between two indexes
# when there is no update.


def find_ans(ar, j, k):
    print(sum(ar[j:k+1]))


ar = [1, 2, 3, 4, 5]
find_ans(ar, 1, 3)
find_ans(ar, 2, 4)

Output

9
12

Time Complexity: O(n), where n represents the size of the given array.
Auxiliary Space: O(1)