function BREADTH-FIRST-SEARCH(problem) returns a solution, or failure
node ← a node with STATE = problem.INITIAL-STATE, PATH-COST = 0
if problem.GOAL-TEST(node.STATE) then return SOLUTION(node)
frontier ← a FIFO queue with node as the only element
explored ← an empty set
loop do
if EMPTY?(frontier) then return failure
node ← POP(frontier) /* chooses the shallowest node in frontier */
add node.STATE to explored
for each action in problem.ACTIONS(node.STATE) do
child ← CHILD-NODE(problem,node,action)
if child.STATE is not in explored or frontier then
if problem.GOAL-TEST(child.STATE) then return SOLUTION(child)
frontier ← INSERT(child,frontier)
Figure ?? Breadth-first search on a graph.