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:

You may assume that the array does not change.
There are many calls to sumRange function.

 1 public class NumArray {
 2     private int[] sum;
 3     public NumArray(int[] nums) {
 4         sum = new int[nums.length+1];
 5         for(int i = 1; i < sum.length; i++)
 6             sum[i] = sum[i-1] + nums[i-1];
 7     }
 8 
 9     public int sumRange(int i, int j) {
10         return sum[j+1] - sum[i];
11     }
12 }
13 
14 
15 // Your NumArray object will be instantiated and called as such:
16 // NumArray numArray = new NumArray(nums);
17 // numArray.sumRange(0, 1);
18 // numArray.sumRange(1, 2);

注意边界