303. Range Sum Query - Immutable

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:

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

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

  int sumRange(int i, int j) {
    if (i == 0){
      return subSum[j];
    }
    else{
      return subSum[j] - subSum[i - 1];
    }
  }

  vector<int>subSum;
};



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