303. Range Sum Query

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.

public class NumArray {
    private int[] sum;
    public NumArray(int[] nums) {
        sum = new int[nums.length+1];
        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];
    }
}


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

注意边界