[LeetCode] 261. Graph Valid Tree

 Problem: https://leetcode.com/problems/graph-valid-tree/

Use DFS to locate if all nodes are connected and no loop exists.

class Solution:
    def validTree(self, n: int, edges: List[List[int]]) -> bool:
        
        seen = [False] * n
        visited = 0
        stack = [0]
        
        graph = defaultdict(set)
        
        for a, b in edges:
            graph[a].add(b)
            graph[b].add(a)
        
        while stack:
            a = stack.pop()
            
            if seen[a]:
                return False
            
            visited += 1
            seen[a] = True
            
            for b in graph[a]:
                stack.append(b)
                graph[b].remove(a)
            
        
        return visited == n