765. Couples Holding Hands

leetcode765.swift

class Solution {
    func minSwapsCouples(_ row: [Int]) -> Int {
        
        var indices = row
        var row = row
        
        for i in 0..<row.count {
            indices[row[i]] = i
        }

        var result = 0
        for i in stride(from: 1, to: row.count-2, by: 2) {
            let a = row[i-1]
            let b = row[i]
            
            if isCouple(a,b) {
                continue
            } else {
                let p = pair(to: b)
                row.swapAt(i-1,indices[p])
                indices.swapAt(p,a)

                result += 1
            }
        }
        return result
    }
    
    func isCouple(_ a: Int, _ b: Int) -> Bool {
        return pair(to: a) == b
    }
    
    func pair(to n:Int) -> Int {
        if n % 2 == 1 {
            return n - 1
        } else {
            return n + 1
        }
    }
}