DFS_graph.py

def DFS(adj):
    def dfs_visit(node, result=None):
        if result == None:
            result = []
        for neighbor in adj[node]:
            if neighbor not in seen:
                result.append(neighbor)
                seen.add(neighbor)
                dfs_visit(neighbor, result)
        return result
    parent = ['A'] # for recording dfs result starting from vertex 'A'
    seen = set()
    parent.extend(dfs_visit('A'))
    return parent
# adjacency list for the graph
adj = {'A':['B','D'], 'B':['C','D'], 'C':[], 'D':['E'], 'E':[]}