var map = [Range:Int]()

func sumRange(_ nums: [Int]) {

    for i in 0..<nums.count {
        var sum = 0

        var j = i

        while j < nums.count {
            sum += nums[j]
            map[Range(i, j)] = sum
            j += 1
        }
    }
}

var nums = [-2, 0, 3, -5, 2, -1]
sumRange(nums)

let range = Range(0, 5)
if let r = map[range] {
    print(r)
}