Graph Valid Tree

def validTree(n, edges):
    if not n:
        return True
    
    adj = {i: [] for i in range(n)}
    for n1, n2 in edges:
        adj[n1].append(n2)
        adj[n2].append(n1)
        
    visit = set()
    
    def dfs(i, prev):
        if i in visit:
            return False
            
        visit.add(i)
        for j in adj[i]:
            if j == prev:
                continue
            if not dfs(j, i):
                return False
        return True
        
    return dfs(0, -1) and n == len(visit)