# Number of Equivalent Domino Pairs in Python

PythonServer Side ProgrammingProgramming

Suppose we have a list of dominos. Each domino has two numbers. Two dominos D[i] = [a, b] and D[j] = [c, d] will be same if a = c and b = d, or a = d and b = c. So one domino can be reversed. We have to return number of pairs (i, j) for which 0 <= i < j < length of Dominos, and determine D[i] is equivalent to D[j]. So if the domino list is like [[1, 2], [2, 1], [3, 4], [6, 5]]. The output will be 1

To solve this, we will follow these steps −

• for each pair p in dominos list −
• sort pair p
• Then store the frequency of each domino into D
• for b in values in D −

## Example

Let us see the following implementation to get better understanding −

Live Demo

class Solution(object):
def numEquivDominoPairs(self, dominoes):
d = {}
ans = 0
for i in dominoes:
i.sort()
i = tuple(i)
if i not in d:
d[i]= 1
else:
d[i]+=1
for b in d.values():
ans += ((b*(b-1))//2)
return ans
ob1 = Solution()
print(ob1.numEquivDominoPairs([[1,2],[2,1],[3,4],[5,6], [4,3]]))

## Input

[[1,2],[2,1],[3,4],[5,6],[4,3]]

## Output

2