Range Sum Query - Immutable

感觉我们是困了。。。

public class NumArray {

    int [] sum = null;
    public NumArray(int[] nums) {
        sum = new int[nums.length];
        for (int i = 0; i < nums.length; i++) {
            //sum[i] = sum[i] + nums[i];
            if (i > 0) {
                sum[i] = sum[i - 1] + nums[i];
            } else {
                sum[i] = nums[i];
            }
        }
    }

    public int sumRange(int i, int j) {
        //return sum[j] - sum[i];
        if (i == 0)
        return sum[j];
        else
        return sum[j] - sum[i - 1];
    }
}


// Your NumArray object will be instantiated and called as such:
// NumArray numArray = new NumArray(nums);
// numArray.sumRange(0, 1);
// numArray.sumRange(1, 2);