Optimized List Sum

Author: saurabhchris1

Optimized_List_Sum.py

@@ -0,0 +1,19 @@
+class ListFastSum:
+    def __init__(self, nums):
+        self.nums = nums
+        self.sum_up_to = []
+
+        current_sum = 0
+        for num in nums:
+            current_sum += num
+            self.sum_up_to.append(current_sum)
+
+        # Allows self.sum_up_to[-1] = 0
+        self.sum_up_to.append(0)
+
+    def sum(self, start_idx, end_idx):
+        return self.sum_up_to[end_idx - 1] - self.sum_up_to[start_idx - 1]
+
+
+print(ListFastSum([1, 2, 3, 4, 5, 6, 7]).sum(2, 5))
+# 12 because 3 + 4 + 5 = 12