0303.go

// Source: https://leetcode.com/problems/range-sum-query-immutable
// Title: Range Sum Query - Immutable
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Given an integer array nums, handle multiple queries of the following type:
//
//   Calculate the sum of the elements of nums between indices left and right inclusive where left <= right.
//
// Implement the NumArray class:
//
//   NumArray(int[] nums) Initializes the object with the integer array nums.
//   int sumRange(int left, int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]).
//
// Example 1:
//
//   Input
//     ["NumArray", "sumRange", "sumRange", "sumRange"]
//     [[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]
//
//   Output
//     [null, 1, -1, -3]
//
//   Explanation
//     NumArray numArray = new NumArray([-2, 0, 3, -5, 2, -1]);
//     numArray.sumRange(0, 2); // return (-2) + 0 + 3 = 1
//     numArray.sumRange(2, 5); // return 3 + (-5) + 2 + (-1) = -1
//     numArray.sumRange(0, 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3
//
// Constraints:
//
//   1 <= nums.length <= 10^4
//   -10^5 <= nums[i] <= 10^5
//   0 <= left <= right < nums.length
//   At most 10^4 calls will be made to sumRange.
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package main

/**
 * Your NumArray object will be instantiated and called as such:
 * obj := Constructor(nums);
 * param_1 := obj.SumRange(left,right);
 */

type NumArray struct {
	partialSum []int
}

func Constructor(nums []int) NumArray {
	for i := 1; i < len(nums); i++ {
		nums[i] += nums[i-1]
	}

	return NumArray{
		partialSum: nums,
	}
}

func (this *NumArray) SumRange(left int, right int) int {
	if left == 0 {
		return this.partialSum[right]
	}
	return this.partialSum[right] - this.partialSum[left-1]
}