"""pseudo-code"""
"""
DFS(graph G, start vertex s):
// all nodes initially unexplored
mark s as explored
for every edge (s, v):
if v unexplored:
DFS(G, v)
"""
def dfs(graph, start):
"""The DFS function simply calls itself recursively for every unvisited child of its argument. We can emulate that
behaviour precisely using a stack of iterators. Instead of recursively calling with a node, we'll push an iterator
to the node's children onto the iterator stack. When the iterator at the top of the stack terminates, we'll pop
it off the stack."""
explored, stack = set(), [start]
explored.add(start)
while stack:
v = stack.pop() # the only difference from BFS is to pop last element here instead of first one
for w in graph[v]:
if w not in explored:
explored.add(w)
stack.append(w)
return explored
G = {'A': ['B', 'C'],
'B': ['A', 'D', 'E'],
'C': ['A', 'F'],
'D': ['B'],
'E': ['B', 'F'],
'F': ['C', 'E']}
print(dfs(G, 'A'))