And an array interval

Given an array of integers nums, the array element from the sum of the index i to j within the range of elements (i ≤ j), comprising i, j points.

Example:

Given nums = [-2, 0, 3, -5, 2, -1], the summation function sumRange ()

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

You can assume that the array can not be changed.
Calls sumRange method multiple times

 1 public class T303 {
 2     private int[] sum;
 3     public T303(int[] nums) {
 4         sum = new int[nums.length + 1];
 5         for (int i = 0; i < nums.length; i++) {
 6             sum[i] = sum[i - 1] + nums[i];
 7         }
 8     }
 9 
10     public int sumRange(int i, int j) {
11         return sum[j + 1] - sum[i];
12     }
13 }