动态规划问题

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.

代码：

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;    
};