303 Range Sum Query

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Example:

Given nums = [-2, 0, 3, -5, 2, -1]sumRange(0, 2) -> 1sumRange(2, 5) -> -1sumRange(0, 5) -> -3

Note:

1. You may assume that the array does not change.
2. There are many calls to sumRange function.

class NumArray {public:    NumArray(vector<int> nums) : psum(nums.size()+1, 0){         partial_sum( nums.begin(), nums.end(), psum.begin()+1);    }        int sumRange(int i, int j) {        return psum[j+1] - psum[i];    }private:    vector<int> psum;};