[swift] LeetCode 238. Product of Array Except Self

Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Solve it without division and in O(n).

For example, given [1,2,3,4], return [24,12,8,6].

Follow up:
Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)

func productExceptSelf(_ nums: [Int]) -> [Int] {
    var res = Array(repeating: 1, count: nums.count)
    var i = 0, v = 1

    while i < nums.count-1 {
        res[i+1] = res[i] * nums[i]
        i += 1
    }

    i = nums.count-2
    while i >= 0 {
        v *= nums[i+1]
        res[i] *= v
        i -= 1
    }
    return res
}

func productExceptSelf(_ nums: [Int]) -> [Int] {

var res = Array(repeating: 1, count: nums.count)

var i = 0, v = 1

while i < nums.count-1 {

res[i+1] = res[i] * nums[i]

i += 1

}

i = nums.count-2

while i >= 0 {

v *= nums[i+1]

res[i] *= v

i -= 1

}

return res

}

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