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

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

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


// Your NumArray object will be instantiated and called as such:
// NumArray numArray = new NumArray(nums);
// numArray.sumRange(0, 1);
// numArray.sumRange(1, 2);
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