Given a list of?dominoes,?dominoes[i] = [a, b]?is?equivalent to?dominoes[j] = [c, d]?if and only if either (a == c?and?b == d), or (a == d?and?b == c) - that is, one domino can be rotated to be equal to another domino.

Return?the number of pairs?(i, j)?for which?0 <= i < j < dominoes.length, and?dominoes[i]?is?equivalent to?dominoes[j].

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Example 1:

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

Output: 1

Example 2:

Input: dominoes = [[1,2],[1,2],[1,1],[1,2],[2,2]]

Output: 3

?

Constraints:

• 1 <= dominoes.length <= 4 * 104

• dominoes[i].length == 2

• 1 <= dominoes[i][j] <= 9

找到相同組合的個數(shù)，2,3 跟3,2是一樣的，所以我們就用大小順序放在一起組成字符串，作為hashmap的key，放進(jìn)去，最后一次遍歷value>1 的情況，即可；

下面是代碼：

Runtime:?24 ms, faster than?39.74%?of?Java?online submissions for?Number of Equivalent Domino Pairs.

Memory Usage:?52.4 MB, less than?38.03%?of?Java?online submissions for?Number of Equivalent Domino Pairs.