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### leetcode Count of Range Sum

Given an integer array nums, return the number of range sums that lie in [lower, upper] inclusive. Range sum S(i, j) is defined as the sum of the elements in nums between indices i and j (ij), inclusive.

Note: A naive algorithm of O(_n_2) is trivial. You MUST do better than that.

Example: Given nums = [-2, 5, -1], lower = -2, upper = 2, Return 3. The three ranges are : [0, 0], [2, 2], [0, 2] and their respective sums are: -2, -1, 2.

C++

### Binary indexed tree (Fenwick tree)

(python 版本比C++简洁太多了^ ^,建议看py版本)

C++

Python