LeetCode:Range Sum Query - Immutable

试题：
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.
代码：

class NumArray {
    int[] sums;
    public NumArray(int[] nums) {
        sums = new int[nums.length];
        
        for(int i=0; i<nums.length; i++){
            if(i==0) sums[i] = nums[i];
            else sums[i] = sums[i-1] + nums[i];
        }
        
    }
    
    public int sumRange(int i, int j) {
        return sums[j]-(i==0?0:sums[i-1]);
    }
}

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * int param_1 = obj.sumRange(i,j);
 */