Coin Flip problem

CoinFlip.swift

func runTest() -> Bool {
    let random = Int.random(in: 0...100)
    var coins = Array(repeating: true, count: 20) + Array(repeating: false, count: random)
    let mask = coins
    coins.shuffle()

    var result: [Bool] = []
    for (coin, flip) in zip(coins, mask) {
        result.append(coin != flip)
    }

    let sum = result[0..<20].sum
    let totalSum = result.sum

    return sum == totalSum / 2
}

extension Collection where Element == Bool {
    var sum: Int {
        reduce(0) {
            $0 + ($1 ? 1 : 0)
        }
    }
}

Problem involving 20 face up coins and some unknown number of face down coins. Need to determine how to divide the coins into two groups so that each group has the same number of face up coins. Here I am treating face up coins as true and face down as false. Applying an XOR to each coin with 20 true and the rest false gives a result where the first 20 coins always have half the number of face up coins as the total pile, so you can just take the first 20 coins as one set and the rest as the other.

shuffle() was a handy method I don't think I've used before in Swift.