go: add «2192. All Ancestors of a Node in a Directed Acyclic Graph»

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

go/all-ancestors-of-a-node-in-a-directed-acyclic-graph.go

@@ -0,0 +1,34 @@
+package main
+
+func getAncestors(n int, edges [][]int) [][]int {
+	fromEdges := func() [][]int {
+		neighbours := make([][]int, n)
+
+		for _, edge := range edges {
+			u, v := edge[0], edge[1]
+			neighbours[u] = append(neighbours[u], v)
+		}
+
+		return neighbours
+	}
+
+	neighbours := fromEdges()
+	ancestors := make([][]int, n)
+
+	var dfs func(int, int)
+	dfs = func(ancestor, node int) {
+		for _, next := range neighbours[node] {
+			vertices := ancestors[next]
+			if len(vertices) == 0 || vertices[len(vertices)-1] != ancestor {
+				ancestors[next] = append(ancestors[next], ancestor)
+				dfs(ancestor, next)
+			}
+		}
+	}
+
+	for i := range n {
+		dfs(i, i)
+	}
+
+	return ancestors
+}