feat: find cutpoints

Author: hackfengJam

GraphTheory/src/graph_bridges/FindCutPoints.java

@@ -0,0 +1,72 @@
+package graph_bridges;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+
+public class FindCutPoints {
+
+    private Graph G;
+    private boolean[] visited;
+
+    private int ord[];
+    private int low[];
+    private int cnt;
+
+    private HashSet<Integer> res;
+
+    public FindCutPoints(Graph G) {
+
+        this.G = G;
+        visited = new boolean[G.V()];
+        ord = new int[G.V()];
+        low = new int[G.V()];
+        cnt = 0;
+        res = new HashSet<>();
+
+        for (int v = 0; v < G.V(); v++)
+            if (!visited[v])
+                dfs(v, v);
+    }
+
+    private void dfs(int v, int parent) {
+        visited[v] = true;
+        ord[v] = cnt;
+        low[v] = ord[v];
+        cnt++;
+
+        int child = 0;
+        for (int w : G.adj(v)) {
+            if (!visited[w]) {
+                dfs(w, v);
+                low[v] = Math.min(low[v], low[w]);
+                if (v != parent && low[w] >= ord[v]) {
+                    res.add(v);
+                }
+                child++;
+                if (v == parent && child > 1)
+                    res.add(v);
+            } else if (w != parent) {
+                low[v] = Math.min(low[v], low[w]);
+            }
+        }
+    }
+
+    public HashSet<Integer> result() {
+        return res;
+    }
+
+    public static void main(String[] args) {
+
+        Graph g = new Graph("./GraphTheory/src/graph_bridges/g.txt");
+        FindCutPoints fb = new FindCutPoints(g);
+        System.out.println(fb.result());
+
+        Graph g2 = new Graph("./GraphTheory/src/graph_bridges/g2.txt");
+        FindCutPoints fb2 = new FindCutPoints(g2);
+        System.out.println(fb2.result());
+
+        Graph tree = new Graph("./GraphTheory/src/graph_bridges/tree.txt");
+        FindCutPoints fb3 = new FindCutPoints(tree);
+        System.out.println(fb3.result());
+    }
+}