Range Sum Query - Immutable

Source

• leetcode: 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.

Java

public class NumArray {
    int[] nums;

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

        this.nums = nums;
    }

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

        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);