303. 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.

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class NumArray {
public:
vector <int> v1={0};
NumArray(vector<int> &nums) {
for(int i=0;i<nums.size();++i)
v1.push_back(nums[i]+v1.back());
}

int sumRange(int i, int j) {
return v1[j+1]-v1[i];
}
};

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