[LeetCode]--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.

我最开始用的就是把数组的元素相加，因为知道i，j嘛，可以依次相加，但是这样就会超时。

如果最开始在构造函数里面构造数组的时候就把和都存进去，这样既可。

public class NumArray {

    public int[] nums;

    public NumArray(