Prefix sum

data_structures/array/prefix_sum.py

@@ -0,0 +1,34 @@
+"""
+Prefix sum algorithm
+Complexity = O(N)
+Return array of sums from the queries list.
+For example, if the numbers is [1,2,3,4,5] and queries is [[0,1],[2,3],[4,5]].
+The first element in the queries list(queries[0]) should return summation of elements
+from index 0 to 1 in array numbers.
+"""
+
+def prefix_sum(numbers, queries):
+    prefix = []
+    output = []
+    prefix.append(numbers[0])
+    numbers_index = 1
+    while numbers_index < len(numbers):
+        prefix.append(prefix[numbers_index-1] + numbers[numbers_index])
+        numbers_index += 1
+    queries_index = 0
+    while queries_index < len(queries):
+        if queries[queries_index][0] == 0:
+            output.append(prefix[queries[queries_index][1]])
+        else:
+            output.append(prefix[queries[queries_index][1]] - prefix[queries[queries_index][0]-1])
+        queries_index += 1
+    return output
+
+"""
+test cases
+"""
+print(prefix_sum([3, 0, -2, 6, -3, 2], [[0, 2], [2, 5], [0, 5]]))
+print(prefix_sum([-1000], [[0, 0]]))
+print(prefix_sum([34, 19, 21, 5, 1, 10, 26, 46, 33, 10], [[3, 7], [3, 4], [3, 7], [4, 5], [0, 5]]))
+print(prefix_sum([-4, -18, -22, -14, -33, -47, -29, -35, -50, -19],
+                 [[2, 9], [5, 6], [1, 2], [2, 2], [4, 5]]))