303. Range Sum Query - Immutable

public class NumArray {
    int[] nums;
    public NumArray(int[] nums) {
        this.nums = nums;
        
        for(int i = 1; i < nums.length; i++)
            nums[i] += nums[i - 1];
    
        
    }

    public int sumRange(int i, int j) {
        if(i == 0)
        return nums[j];
    
        return nums[j] - nums[i - 1];
    }
}

 

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