solve graph valid tree

Author: sora0319

graph-valid-tree/sora0319.java

@@ -0,0 +1,40 @@
+public class Solution {
+    public boolean validTree(int n, int[][] edges) {
+        Map<Integer, List<Integer>> graph = new HashMap<>();
+        for (int i = 0; i < n; i++) {
+            graph.put(i, new ArrayList<>());
+        }
+
+        for (int[] edge : edges) {
+            int node = edge[0];
+            int adj = edge[1];
+            graph.get(node).add(adj);
+            graph.get(adj).add(node);
+        }
+
+        Set<Integer> visited = new HashSet<>();
+        if (inCycle(0, -1, graph, visited)) {
+            return false;
+        }
+
+        return visited.size() == n;
+    }
+
+    private boolean inCycle(int node, int prev, Map<Integer, List<Integer>> graph, Set<Integer> visited) {
+        if (visited.contains(node)) {
+            return true;
+        }
+
+        visited.add(node);
+
+        for (int neighbor : graph.get(node)) {
+            if (neighbor == prev) continue;
+            if (inCycle(neighbor, node, graph, visited)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}
+