leetcode NumArray

import java.util.ArrayList;
/*
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.
 */
public class NumArray {
  ArrayList<Integer> sums = new ArrayList<>();
  public NumArray(int[] nums){
    sums.add(0);
    int sum = 0;
    for(int i: nums){
      sum += i;
      sums.add(sum);
    }
  }

  public  int sumRange(int i, int j) {
    return sums.get(j)-sums.get(i);
  }
}