【Leetcode】Range Sum Query - Immutable

题目链接：https://leetcode.com/problems/range-sum-query-immutable/
题目：

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:

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

算法：

 public class NumArray {
     int nums[];
     int sums[];

     public NumArray(int[] nums) {
         this.nums = nums;
         if (nums != null && nums.length != 0) {
             this.sums = new int[nums.length];
             sums[0] = nums[0];
             for (int i = 1; i < sums.length; i++) {
                 sums[i] = sums[i - 1] + nums[i];
             }
         }
     }

     public int sumRange(int i, int j) {
         int sum = sums[j] - sums[i] + nums[i];
         return sum;
     }
 }