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
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
SOLUTION:
class Solution:
def numEquivDominoPairs(self, dominoes: List[List[int]]) -> int:
n = len(dominoes)
ctr = {}
for i in range(n):
curr = tuple(sorted(dominoes[i]))
ctr[curr] = ctr.get(curr, 0) + 1
op = 0
for pair in ctr:
op += ctr[pair] * (ctr[pair] - 1) // 2
return op
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