RangeSumQueryImmutable.java

package com.fishercoder.solutions;

/**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 RangeSumQueryImmutable {

    
}

class NumArray {
    int[] sums;
    public NumArray(int[] nums) {
        sums = new int[nums.length];
        for(int i = 0; i < nums.length; i++){
            if(i == 0){
                sums[i] = nums[i];
            } else {
                sums[i] = sums[i-1] + nums[i];
            }
        }
    }

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