[LeetCode] Problem 303 - Range Sum Query - Immutable

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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.

Code

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private int[] sum;

public NumArray(int[] nums) {
    sum = new int[nums.length + 1];

    for (int i  = 0; i < nums.length; i++)
        sum[i + 1] = sum[i] + nums[i];
}

public int sumRange(int i, int j) {
    return sum[j + 1] - sum[i];
}