N couples sit in 2N seats arranged in a row and want to hold hands. We want to know the minimum number of swaps so that every couple is sitting side by side. A swap consists of choosing any two people, then they stand up and switch seats.
The people and seats are represented by an integer from 0 to 2N-1, the couples are numbered in order, the first couple being (0, 1), the second couple being (2, 3), and so on with the last couple being (2N-2, 2N-1).
The couples' initial seating is given by row[i] being the value of the person who is initially sitting in the i-th seat.
Input: row = [0, 2, 1, 3] Output: 1 Explanation: We only need to swap the second (row) and third (row) person.
Input: row = [3, 2, 0, 1] Output: 0 Explanation: All couples are already seated side by side.
- len(row) is even and in the range of [4, 60].
- row is guaranteed to be a permutation of 0...len(row)-1.
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