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"""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]
while stack:
v = (
stack.pop()
) # one difference from BFS is to pop last element here instead of first one
if v in explored:
continue
explored.add(v)
for w in graph[v]:
if w not in explored:
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"))