number-of-equivalent-domino-pairs

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1128. Number of Equivalent Domino Pairs (Easy)

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].

 

Example 1:

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

 

Constraints:

• 1 <= dominoes.length <= 40000
• 1 <= dominoes[i][j] <= 9

Related Topics

[Array]

Hints

Hint 1

For each domino j, find the number of dominoes you've already seen (dominoes i with i < j) that are equivalent.

Hint 2

You can keep track of what you've seen using a hashmap.