package main

const (
	DIRECT  = 1
	REVERSE = 0
)

type Edge struct {
	neighbor int
	edgeType int
}

func minReorder(n int, connections [][]int) int {
	var dfs func(int, int)
	makeGraph := func() map[int]([]Edge) {
		g := make(map[int]([]Edge))

		for _, edge := range connections {
			u, v := edge[0], edge[1]

			neighbors, present := g[u]
			if !present {
				neighbors = make([]Edge, 0)
			}
			g[u] = append(neighbors, Edge{neighbor: v, edgeType: DIRECT})

			neighbors, present = g[v]
			if !present {
				neighbors = make([]Edge, 0)
			}
			g[v] = append(neighbors, Edge{neighbor: u, edgeType: REVERSE})
		}

		return g
	}

	graph := makeGraph()

	count := 0
	dfs = func(parent, node int) {
		neighbors, found := graph[node]
		if !found {
			return
		}

		for _, edge := range neighbors {
			if edge.neighbor != parent {
				count += edge.edgeType
				dfs(node, edge.neighbor)
			}
		}
	}

	dfs(-1, 0)

	return count
}