LeetCode 303 Range Sum Query - Immutable

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.

话不多说，直接看答案吧。参考了/article/7966850.html

class NumArray {
int[] sums;

public NumArray(int[] nums) {
sums = new int[nums.length];
System.arraycopy(nums, 0, sums, 0, nums.length);
for (int i = 1; i < nums.length; i++)
sums[i] = sums[i - 1] + nums[i];
}

public int sumRange(int i, int j) {
if (i < 0 || j < 0 || i >= sums.length || j >= sums.length) return 0;
return i == 0 ? sums[j] : sums[j] - sums[i - 1];
}
}