def select(array, k):
"""Rearranges the array so that array[k] contains the kth smalles key;
array[0] through array[k-1] are less than (or equal to) array[k]; and
array[k+1] through array[n-1] are greather than (or equal to) array[k]
:param array: the array
:param k: the rank of the key
:return: the key of rank k
"""
stdrandom.shuffle(array)
lo = 0
hi = len(array) - 1
while hi > lo:
i = _partition(array, lo, hi)
if i > k:
hi = i - 1
elif i < k:
lo = i + 1
else:
return array[i]
return array[lo]
def main(args):
from itu.algs4.stdlib import stdrandom as stdrandom
# create random DAG with V vertices and E edges; then add F random edges
V = int(args[0])
E = int(args[1])
F = int(args[2])
G = EdgeWeightedDigraph(V)
vertices = [i for i in range(V)]
stdrandom.shuffle(vertices)
for _ in range(E):
while True:
v = stdrandom.uniformInt(0, V)
w = stdrandom.uniformInt(0, V)
if v >= w:
break
weight = stdrandom.uniformFloat(0.0, 1.0)
G.add_edge(DirectedEdge(v, w, weight))
# add F extra edges
for _ in range(F):
v = stdrandom.uniformInt(0, V)
w = stdrandom.uniformInt(0, V)
weight = stdrandom.uniformFloat(0.0, 1.0)
G.add_edge(DirectedEdge(v, w, weight))
print(G)
# find a directed cycle
finder = EdgeWeightedDirectedCycle(G)
if finder.has_cycle():
print("Cycle: ")
for e in finder.cycle():
print("{} ".format(e), end="")
print()
# or give topologial sort
else:
print("No directed cycle")
def sort(array):
"""Rearranges the array in ascending order, using the natural order."""
stdrandom.shuffle(array)
_sort(array, 0, len(array) - 1)
def is_sorted(array):
return _is_sorted(array, 0, len(array) - 1)
def _is_sorted(array, lo, hi):
for i in range(lo + 1, hi + 1):
if array[i] < array[i - 1]:
return False
return True
# print array to standard output
def show(array):
stdio.write(" ".join(array))
if __name__ == "__main__":
array = stdio.readAllStrings()
sort(array)
assert is_sorted(array)
show(array)
# shuffle
stdrandom.shuffle(array)
# display results again using select
print()
for i in range(0, len(array)):
ith = str(select(array, i))
stdio.writeln(ith)