Solve Graph Valid Tree

Author: bky373

graph-valid-tree/bky373.java

@@ -0,0 +1,42 @@
+/*
+    time: O(n + m), where n is the number of nodes and m is the number of edges in the graph.
+    space: O(n + m)
+ */
+class Solution {
+
+    public boolean validTree(int n, int[][] edges) {
+
+        if (edges.length != n - 1) {
+            return false;
+        }
+
+        List<List<Integer>> adjList = new ArrayList<>();
+        for (int i = 0; i < n; i++) {
+            adjList.add(new ArrayList<>());
+        }
+        for (int[] edge : edges) {
+            adjList.get(edge[0])
+                   .add(edge[1]);
+            adjList.get(edge[1])
+                   .add(edge[0]);
+        }
+
+        Stack<Integer> stack = new Stack<>();
+        Set<Integer> visited = new HashSet<>();
+        stack.push(0);
+        visited.add(0);
+
+        while (!stack.isEmpty()) {
+            int curr = stack.pop();
+            for (int adj : adjList.get(curr)) {
+                if (visited.contains(adj)) {
+                    continue;
+                }
+                visited.add(adj);
+                stack.push(adj);
+            }
+        }
+
+        return visited.size() == n;
+    }
+}