参考文献

区域检索，前缀和的应用，注意下标的映射，前缀和一般从1开始

C++ 代码

class NumArray {
public:
    vector<int> prefix_sum_;
    NumArray(vector<int>& nums) {
        int n = nums.size();
        // 下标从1开始
        prefix_sum_ = vector(n+1, 0);
        for(int i=1; i<=n; ++i)prefix_sum_[i] = prefix_sum_[i-1] + nums[i-1];
    }

    int sumRange(int left, int right) {
        ++left, ++right;
        return prefix_sum_[right] - prefix_sum_[left-1];
    }
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray* obj = new NumArray(nums);
 * int param_1 = obj->sumRange(left,right);
 */