In a row of dominoes, A[i] and B[i] represent the top and bottom halves of the i-th domino. (A domino is a tile with two numbers from 1 to 6 - one on each half of the tile.)

We may rotate the i-th domino, so that A[i] and B[i] swap values.

Return the minimum number of rotations so that all the values in A

If it cannot be done, return -1.

Example 1:

Input: A = [2,1,2,4,2,2], B = [5,2,6,2,3,2]
Output: 2
Explanation: 
The first figure represents the dominoes as given by A and B: before we do any rotations.
If we rotate the second and fourth dominoes, we can make every value in the top row equal to 2, as indicated by the second figure.
 

Example 2:

Input: A = [3,5,1,2,3], B = [3,6,3,3,4]
Output: -1
Explanation: 
In this case, it is not possible to rotate the dominoes to make one row of values equal.

Note:

1. 1 <= A[i], B[i] <= 6
2. 2 <= A.length == B.length <= 20000

在一排多米諾骨牌中，A[i] 和 B[i] 分別代表第 i 個多米諾骨牌的上半部分和下半部分。（一個多米諾是兩個從 1 到 6 的數字同列平鋪形成的 —— 該平鋪的每一半上都有一個數字。）

我們可以旋轉第 i 張多米諾，使得 A[i] 和 B[i] 的值交換。

返回能使 A 中所有值或者 B 中所有值都相同的最小旋轉次數。

如果無法做到，返回 -1.

示例 1：

輸入：A = [2,1,2,4,2,2], B = [5,2,6,2,3,2]
輸出：2
解釋：
圖一表示：在我們旋轉之前， A 和 B 給出的多米諾牌。
如果我們旋轉第二個和第四個多米諾骨牌，我們可以使上面一行中的每個值都等於 2，如圖二所示。

示例 2：

輸入：A = [3,5,1,2,3], B = [3,6,3,3,4]
輸出：-1
解釋：
在這種情況下，不可能旋轉多米諾牌使一行的值相等。

提示：

1. 1 <= A[i], B[i] <= 6
2. 2 <= A.length == B.length <= 20000

 1 class Solution {
 2     func minDominoRotations(_ A: [Int], _ B: [Int]) -> Int {
 3         var n:Int = A.count
 4         var best:Int = Int.max
 5         for same in 1...6
 6         {
 7             var a_cost:Int = 0
 8             var b_cost:Int = 0
 9             
10             for i in 0..<n
11             {
12                 if A[i] != same && B[i] != same
13                 {
14                     a_cost = Int.max
15                     b_cost = Int.max
16                     break;
17                 }
18                 if A[i] != same
19                 {
20                     a_cost += 1
21                 }
22                 if B[i] != same
23                 {
24                     b_cost += 1
25                 }
26             }
27             best = min(best, min(a_cost, b_cost))
28         }
29         return best < Int.max / 2 ? best : -1        
30     }
31 }

[Swift Weekly Contest 127]LeetCode1007. 行相等的最少多米諾旋轉 | Minimum Domino Rotations For Equal Row