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.
public class NumArray { int[] sum; public NumArray(int[] nums) { if (nums == null || nums.length == 0) { return; } sum = new int[nums.length]; sum[0] = nums[0]; for (int i = 1; i < nums.length; i++) { sum[i] = sum[i - 1] + nums[i]; } } public int sumRange(int i, int j) { return i == 0 ? sum[j] : sum[j] - sum[i - 1]; } }