Prefix sum

algorithms/math/two-sums

@@ -0,0 +1,20 @@
+"""
+Complexity = O(N*M) 
+Given an Array of Integers
+return the index of the two numbers which their sum is equals 
+to the  target
+
+"""
+def twoSum(nums, target):
+    i = 0
+    flag = False
+    for i in range(len(nums)):
+        if(flag):
+            break
+        for j in range(len(nums)):
+            if( i !=j ):
+                if(nums[i] + nums[j] == target):
+                      print(str(i) + " " + str(j))
+                      flag = True
+
+

data_structures/array/prefix_sum.py

@@ -0,0 +1,31 @@
+#prefix sum algorithm
+
+#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.
+#time complexity O(n)
+
+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]]))