骰子问题

func findDic(_ dics:[[Character]], _ str: String) -> [[Int]]{

    //生成一个 char 对 set of dic index的 dictionary
    var map = [Character: Set<Int>]() // char - list of dic(index)
    for (index, dic) in dics.enumerated(){
        for char in dic{
            map[char, default: Set<Int>()].insert(index)
        }
    }

    //对于每个位置开始dfs (start with 0)
    let arr = Array(str)
    var visited = Set<Int>()
    var curr = [Int]()
    var result = [[Int]]()
    print(map)
    dfs(map, &visited, arr, 0, &curr, &result)
    return result

}
func dfs(_ map: [Character: Set<Int>], _ visited: inout  Set<Int>, _ arr: [Character], _ start: Int, _ curr : inout [Int], _ result: inout [[Int]]){
    if start == arr.count{
        result.append(curr)
        return
    }
    if let list = map[arr[start]]{
        for index in list{
            if !visited.contains(index) {
                visited.insert(index)
                curr.append(index)
                dfs(map, &visited, arr, start + 1, &curr, &result)
                curr.removeLast()
                visited.remove(index)
            }
        }
    }
}


let dice : [Character] = ["A","B","A"]
let dice2 : [Character] = ["B","B","B"]
let dice3 : [Character] = ["C","D","A"]

let dices = [dice, dice2, dice3]
print(findDic(dices, "ABC"))