go: add «1466. Reorder Routes to Make All Paths Lead to the City Zero»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/reorder-routes-to-make-all-paths-lead-to-the-city-zero.go

@@ -0,0 +1,57 @@
+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
+}