Description

Submission

class NumArray {
    vector<int> presum;
public:
    NumArray(vector<int>& nums) {
        nums.insert(nums.begin(), 0);
        int n = nums.size();
        presum.resize(n);
        presum[0] = 0;
        for(int i = 1; i < n; ++i) {
            presum[i] = presum[i-1] + nums[i];
        }
    }
    
    int sumRange(int left, int right) {
        return presum[right+1] - presum[left];
    }
};

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