[LeetCode] 303. Range Sum Query - Immutable

Problem

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

Solution

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