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.

 1 public class NumArray {
 2     int[] leftSums;
 3 
 4     public NumArray(int[] nums) {
 5         leftSums = new int[nums.length];
 6         if (nums.length == 0) return;
 7         leftSums[0] = nums[0];
 8         for (int i=1; i<nums.length; i++) {
 9             leftSums[i] = leftSums[i-1] + nums[i];
10         }
11     }
12 
13     public int sumRange(int i, int j) {
14         return i==0? leftSums[j] : leftSums[j] - leftSums[i-1];
15     }
16 }
17 
18 
19 // Your NumArray object will be instantiated and called as such:
20 // NumArray numArray = new NumArray(nums);
21 // numArray.sumRange(0, 1);
22 // numArray.sumRange(1, 2);