Check if a given graph is tree or not.java

class Solution {
    static boolean solve(ArrayList<ArrayList<Integer>> graph,int parent,int curr,boolean visited[]) {
        //mark curr node True
        visited[curr] = true;
        
        for(int i: graph.get(curr)) {
            //since the graph is bidirectional so we have to avoid to visit parent again
            if(i == parent) continue;
            //if the current node is already visited that means cycle is present in the graph
            if(visited[i]) return false;
            // traverse for rest of the node
            if(!solve(graph,curr,i,visited))return false;
        }
        // if cycle is not detected in the graph that means the graph is also a tree
        return true;
    }
    public boolean isTree(int n, int m, ArrayList<ArrayList<Integer>> edges) 
    {   
        ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
        for(int i=0; i<n; i++) graph.add(new ArrayList<>());
        //Creating a adjacency matrix from a arraylist
        for(ArrayList<Integer> i : edges) {
            graph.get(i.get(0)).add(i.get(1));
            graph.get(i.get(1)).add(i.get(0));
        }
        
        boolean visited[] = new boolean[n];
        boolean ans = solve(graph,-1,0,visited);
        // To check all graph node are connected or not
        for(int i=0; i<n; i++) if(!visited[i]) return false;
        
        return ans;
    }
}