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// @Title: 情侣牵手 (Couples Holding Hands)
// @Author: 15816537946@163.com
// @Date: 2021-02-14 21:37:52
// @Runtime: 0 ms
// @Memory: 2 MB
// 并查集，情人节撒狗粮呢

type unionFind struct {
	parent, size []int
	setCount     int // 当前连通分量数目
}

func newUnionFind(n int) *unionFind {
	parent := make([]int, n)
	size := make([]int, n)
	for i := range parent {
		parent[i] = i
		size[i] = 1
	}
	return &unionFind{parent, size, n}
}

func (uf *unionFind) find(x int) int {
	if uf.parent[x] != x {
		uf.parent[x] = uf.find(uf.parent[x])
	}
	return uf.parent[x]
}

func (uf *unionFind) union(x, y int) {
	fx, fy := uf.find(x), uf.find(y)
	if fx == fy {
		return
	}
	if uf.size[fx] < uf.size[fy] {
		fx, fy = fy, fx
	}
	uf.size[fx] += uf.size[fy]
	uf.parent[fy] = fx
	uf.setCount--
}

func minSwapsCouples(row []int) int {
	n := len(row)
	uf := newUnionFind(n / 2)
	for i := 0; i < n; i += 2 {
		uf.union(row[i]/2, row[i+1]/2)
	}
	return n/2 - uf.setCount
}