輸入：dominoes = [[1,2],[2,1],[3,4],[5,6]]
輸出：1

struct KEY
{
    int minNum;
    int maxNum;
    KEY(int f,int s):minNum(f),maxNum(s){}
};
struct HashFunc
{
    size_t operator()(const KEY& key) const
    {
        return ((hash<int>()(key.minNum) ^ (hash<int>()(key.maxNum) << 1)) >> 1);
    }
};
struct EqualKey
{
	bool operator () (const KEY &lhs, const KEY &rhs) const
	{
		return lhs.minNum  == rhs.minNum && lhs.maxNum == rhs.maxNum;
	}
};
class Solution {
public:
    int numEquivDominoPairs(vector<vector<int>>& dominoes) {
        unordered_map<KEY,int,HashFunc,EqualKey> um;
        int count = 0;
        int maxNum = 0,minNum = 0;
        for(auto &n : dominoes)
        {
            minNum = min(n[0],n[1]);
            maxNum = max(n[0],n[1]);
            if(um.find({minNum,maxNum}) != um.end())
            {
                count += um[{minNum,maxNum}];
                um[{minNum,maxNum}]++;
            }
            else
            {
                um[{minNum,maxNum}]++;
            }
        }
        return count;
    }
};

class Solution:
    def numEquivDominoPairs(self, dominoes: List[List[int]]) -> int:
        ans = 0
        d = dict()
        for d1, d2 in dominoes:
            # 排序后加入字典
            index = tuple(sorted((d1, d2)))
            if index in d:
                d[index] += 1
            else:
                d[index] = 1
        # 計算答案
        for i in d:
            ans += d[i] * (d[i] - 1) // 2
        return ans

class Solution:
    def numEquivDominoPairs(self, dominoes: List[List[int]]) -> int:
        dominoes_new = []
        for i in dominoes:
            a = i[0]
            b = i[1]
            if a > b:
                a, b = b, a
            dominoes_new.append(a*10+b)
        Hash = {}
        for j in dominoes_new:
            Hash[j] = Hash.get(j, 0) + 1
        res = 0
        for key in Hash.keys():
            n = Hash[key]
            res += n*(n-1)//2
        return res