Caculate sum of a range quickly

See all series problems: #presum

- Leetcode: Subarray Sums Divisible by K
- Leetcode: Subarray Sum Equals K
- Leetcode: Remove Zero Sum Consecutive Nodes from Linked List
- Leetcode: Range Sum Query – Immutable
- Leetcode: Random Pick with Weight
- Leetcode: Maximum Sum of Two Non-Overlapping Subarrays
- Leetcode: Maximum Subarray
- Leetcode: Maximum Size Subarray Sum Equals k
- Leetcode: Maximum Product Subarray
- Leetcode: Count Number of Nice Subarrays

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