// 不使用线段树的解决方案
class NumArray {

    private int[] sum; // sum[i]存储前i个元素和， sum[0] = 0                   
    public NumArray(int[] nums) {
        sum = new int[nums.length + 1]; // sum[i]存储nums[0....i-1]的和 
        sum[0] = 0;
        for(int i = 1; i <sum.length; i++){
            sum[i] = sum[i - 1] + nums[i - 1];
        }
    }
    
    public int sumRange(int i, int j) {
        return sum[j + 1] - sum[i]; // 0到j的和 减去 0到i-1的和，剩下的就是i到j的和
    }
}

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