Create routers articulation point

static int time = 0; public static void main(String[] args) { int numRouters1 = 5; int numLinks1 = 6; int[][] links1 = {{0, 1}, {1, 2}, {0, 2}, {2, 3}, {2, 4}, {3, 4}}; System.out.println(getCriticalNodes(links1, numLinks1, numRouters1)); int numRouters2 = 5; int numLinks2 = 5; int[][] links2 = {{0, 1}, {1, 2}, {0, 2}, {0, 3}, {3, 4}}; System.out.println(getCriticalNodes(links2, numLinks2, numRouters2)); int numRouters3 = 4; int numLinks3 = 3; int[][] links3 = {{0, 1}, {1, 2}, {2, 3}}; System.out.println(getCriticalNodes(links3, numLinks3, numRouters3)); int numRouters4 = 7; int numLinks4 = 7; int[][] links4 = {{0, 1}, {0, 2}, {1, 3}, {2, 3}, {2, 5}, {5, 6}, {3, 4}}; System.out.println(getCriticalNodes(links4, numLinks4, numRouters4)); } private static List<Integer> getCriticalNodes(int[][] links, int numLinks, int numRouters) { time = 0; Map<Integer, Set<Integer>> map = new HashMap<>(); for(int i=0;i<numRouters;i++) { map.put(i, new HashSet<>()); } for(int[] link : links) { map.get(link[0]).add(link[1]); map.get(link[1]).add(link[0]); } List<Integer> res = new ArrayList<>(); int[] low = new int[numRouters]; int[] ids = new int[numRouters]; int parent[] = new int[numRouters]; Arrays.fill(ids, -1); Arrays.fill(parent, -1); for(int i=0;i<numRouters;i++) { if(ids[i] == -1) dfs(map, low, ids, parent, i, res); } return res; } private static void dfs(Map<Integer, Set<Integer>> map, int[] low, int[] ids, int[] parent, int cur, List<Integer> res) { int children = 0; ids[cur] = low[cur]= ++time; for(int nei : map.get(cur)) { if(ids[nei] == -1) { children++; parent[nei] = cur; dfs(map, low, ids, parent,nei, res); low[cur] = Math.min(low[cur], low[nei]); if((parent[cur] == -1 && children > 1) || (parent[cur] != -1 && low[nei] >= ids[cur])) res.add(cur); } else if(nei != parent[cur]) low[cur] = Math.min(low[cur], ids[nei]); } }