leetcode-78-subsets.swift

/**

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https://leetcode.com/problems/subsets/


Given a set of distinct integers, nums, return all possible subsets (the power set).

Note: The solution set must not contain duplicate subsets.

Example:

Input: nums = [1,2,3]
Output:
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

*/

/**
Big O Annotation
Time complexity O(2^n) where n is the amount of elements in nums.
Space complexity O(n) where n is the amount of elements in nums.
*/
func subsets(_ nums: [Int]) -> [[Int]] {
        
    // Create the output array
    var subsets: [[Int]] = []

    // Add all subsets
    add(&subsets, for: nums)

    // And returns        
    return subsets
}

private func add(_ subsets: inout [[Int]], for numbers: [Int], startAt index: Int = 0, current: [Int] = []) {

    // Add the current value of current to the output
    subsets.append(current)

    // Get a mutable copy of current
    var current = current
    
    // Iterate through the remaining indices
    for i in index..<numbers.count {

        // Add the current number
        current.append(numbers[i])

        // Recursivly call again
        add(&subsets, for: numbers, startAt: i + 1, current: current)

        // And also remove the number
        current.remove(at: current.count - 1)
    }
}