261. Graph Valid Tree

class Solution:
    def validTree(self, n, edges):
        """
        :type n: int
        :type edges: List[List[int]]
        :rtype: bool
        """
        if len(edges) != n-1:
            return False

        neighbors = {}
        for i in range(n):
            neighbors[i] = []

        for v1, v2 in edges:
            neighbors[v1].append(v2)
            neighbors[v2].append(v1)

        st = [0]
        while st:
            node = st.pop()
            nodes = neighbors.pop(node, [])
            st.extend(nodes)

        return not neighbors