[Leetcode]Range Sum Query - Immutable

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) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

Note:

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

class NumArray {
private:
vector<int>sumArray;
public:
NumArray(vector<int> &nums) {
int sum = 0;
for(int i = 0;i < nums.size();i++){
sum += nums[i];
sumArray.push_back(sum);
}
}

int sumRange(int i, int j) {
int ret = sumArray[j];
if(i > 0){
ret -= sumArray[i-1];
}
return ret;
}
};

// Your NumArray object will be instantiated and called as such:
// NumArray numArray(nums);
// numArray.sumRange(0, 1);
// numArray.sumRange(1, 2);