数据结构与算法python语言实现-第五章答案
数据结构与算法python语言实现-第五章答案
5.2
import sys
try:
n = int(sys.argv[1])#接收命令行参数
except:
n = 100
import sys # provides getsizeof function
data = []
for k in range(n): # NOTE: must fix choice of n
a = len(data) # number of elements
b = sys.getsizeof(data) # actual size in bytes
if not b-8*a-64:
print('Length: {0:3d}; Size in bytes: {1:4d}'.format(a, b))
data.append(None) # increase length by one
5.4
import ctypes # provides low-level arrays
class DynamicArray:
"""A dynamic array class akin to a simplified Python list."""
def __init__(self):
"""Create an empty array."""
self._n = 0 # count actual elements
self._capacity = 1 # default array capacity
self._A = self._make_array(self._capacity) # low-level array
def __len__(self):
"""Return number of elements stored in the array."""
return self._n
def __getitem__(self, k):
"""Return element at index k."""
if -1*self._n < k < 0:
return self._A[self._n +k] # retrieve from array
elif 0 <= k < self._n:
return self._A[k] # retrieve from array
else:
raise IndexError('invalid index')
def append(self, obj):
"""Add object to end of the array."""
if self._n == self._capacity: # not enough room
self._resize(2 * self._capacity) # so double capacity
self._A[self._n] = obj
self._n += 1
def _resize(self, c): # nonpublic utitity
"""Resize internal array to capacity c."""
B = self._make_array(c) # new (bigger) array
for k in range(self._n): # for each existing value
B[k] = self._A[k]
self._A = B # use the bigger array
self._capacity = c
def _make_array(self, c): # nonpublic utitity
"""Return new array with capacity c."""
return (c * ctypes.py_object)() # see ctypes documentation
def insert(self, k, value):
"""Insert value at index k, shifting subsequent values rightward."""
# (for simplicity, we assume 0 <= k <= n in this verion)
if self._n == self._capacity: # not enough room
self._resize(2 * self._capacity) # so double capacity
for j in range(self._n, k, -1): # shift rightmost first
self._A[j] = self._A[j - 1]
self._A[k] = value # store newest element
self._n += 1
def remove(self, value):
"""Remove first occurrence of value (or raise ValueError)."""
# note: we do not consider shrinking the dynamic array in this version
for k in range(self._n):
if self._A[k] == value: # found a match!
for j in range(k, self._n - 1): # shift others to fill gap
self._A[j] = self._A[j + 1]
self._A[self._n - 1] = None # help garbage collection
self._n -= 1 # we have one less item
return # exit immediately
raise ValueError('value not found') # only reached if no match
A = DynamicArray()
for j in range(6):
A.append(j)
for j in range(6):
print(A[j])
print('\n',A[-2])
5.5
从k扩大到2k需3k，开销还包括从k/2到k的历次append，为k/2。
硬币应该在k/2到k的阶段收取完毕
开销为3k+k/2
收费次数为k-k/2=k/2
每次收费为(3k+k/2)/(k/2)=7
后半部分到扩大为一个周期。
5.6
import ctypes # provides low-level arrays
class DynamicArray:
"""A dynamic array class akin to a simplified Python list."""
def __init__(self):
"""Create an empty array."""
self._n = 0 # count actual elements
self._capacity = 1 # default array capacity
self._A = self._make_array(self._capacity) # low-level array
def __len__(self):
"""Return number of elements stored in the array."""
return self._n
def __getitem__(self, k):
"""Return element at index k."""
if -1 * self._n < k < 0:
return self._A[self._n + k] # retrieve from array
elif 0 <= k < self._n:
return self._A[k] # retrieve from array
else:
raise IndexError('invalid index')
def append(self, obj):
"""Add object to end of the array."""
if self._n == self._capacity: # not enough room
self._resize(2 * self._capacity) # so double capacity
self._A[self._n] = obj
self._n += 1
def _resize(self, c): # nonpublic utitity
"""Resize internal array to capacity c."""
B = self._make_array(c) # new (bigger) array
for k in range(self._n): # for each existing value
B[k] = self._A[k]
self._A = B # use the bigger array
self._capacity = c
def _make_array(self, c): # nonpublic utitity
"""Return new array with capacity c."""
return (c * ctypes.py_object)() # see ctypes documentation
def insert(self, k, value):
"""Insert value at index k, shifting subsequent values rightward."""
# (for simplicity, we assume 0 <= k <= n in this verion)
if self._n == self._capacity: # not enough room
B = self._A[0:k]
B.append(value)
for j in range(k, self._n):
B.append(self._A[j])
self._A = B
self._n += 1
else:
for j in range(self._n, k, -1): # shift rightmost first
self._A[j] = self._A[j - 1]
self._A[k] = value # store newest element
self._n += 1
def remove(self, value):
"""Remove first occurrence of value (or raise ValueError)."""
# note: we do not consider shrinking the dynamic array in this version
for k in range(self._n):
if self._A[k] == value: # found a match!
for j in range(k, self._n - 1): # shift others to fill gap
self._A[j] = self._A[j + 1]
self._A[self._n - 1] = None # help garbage collection
self._n -= 1 # we have one less item
return # exit immediately
raise ValueError('value not found') # only reached if no match
A = DynamicArray()
for j in range(4):
A.append(j)
A.insert(2, 6)
for j in range(5):
print(A[j])
5.7
def find(A,n):
return sum(A)-sum(range(n))
A=(1,2,3,4,4,5,6)
print(find(A,7))
5.8
from time import time
N=10000
list = [j for j in range(N)]
start = time()
while list:
list.pop(0)
end = time()
print((end - start) / N)
list = [j for j in range(N)]
start = time()
while list:
list.pop(len(list) // 2)
end = time()
print((end - start) / N)
list = [j for j in range(N)]
start = time()
while list:
list.pop(len(list)-1)
end = time()
print((end - start) / N)
5.26
def find_repetition(seq):
seq=sorted(seq)
a=[]
for i in range(len(seq)-1):
if seq[i]== seq[i+1]:
a.append(seq[i])
return a
def sorted(seq):
for i in range(len(seq) - 1):
for j in range(len(seq) - i-1):
if seq[j] > seq[j + 1]:
seq[j], seq[j + 1] = seq[j + 1], seq[j]
return seq
seq=[0,2,2,3,5,6,4,8,6,6,4,4,3,41]
print(find_repetition(seq))
5.27
def find(seq,n):
for i in range(len(seq)):
if n==seq[i]:
return False
return True
def construct_seq(seq):
for i in range(len(seq)):
seq[i]=bin(seq[i])
return seq
def bin(data):
result=''
if data :
result=bin(data//2)
return result+str(data%2)
else:
return result
a=[2,35,14,23,33,55]
a=construct_seq(a)
print(a)
print(find(a,'00'))
附栈实现进制转换
def bin2(data):
result=[]
while data :
result.append(data%2)
data=data//2
result.reverse()
return result
a=56
print(bin2(a))
递归实现进制转换
def bin(data):
result=''
if data :
result=bin(data//2)
return result+str(data%2)
else:
return result