python代码实现
冒泡排序
def buble_sort(alist):
"""冒泡排序"""
n = len(alist)
for j in range(n-1):
# 要走多少趟
count = 0
for i in range(0, n-1-j):
# 从头走到尾要走多少次
if alist[i] > alist[i+1]:
alist[i], alist[i+1] = alist[i+1], alist[i]
count += 1
if count == 0:
return
选择排序
def select_sort(alist):
"""选择排序"""
n = len(alist)
for j in range(0, n-1):
min_index = j
for i in range(j+1, n):
if alist[min_index] > alist[i]:
min_index = i
alist[j], alist[min_index] = alist[min_index], alist[j]
插入排序
def insert_sort(alist):
"""插入排序"""
n = len(alist)
# 从右边的无序序列中取出多少个元素执行这样的过程
for j in range(1, n):
# j = [1, 2, 3, n-1]
# i 代表内层循环起始值
i = j
# 执行从右边的无序序列中取出第一个元素，即i位置的元素，然后将其插入到前面的正确位置中
while i > 0:
if alist[i] < alist[i-1]:
alist[i], alist[i-1] = alist[i-1], alist[i]
i -= 1
else:
break
希尔排序
def shell_sort(alist):
"""希尔排序"""
# n=9
n = len(alist)
# gap =4
gap = n // 2
# i = gap
# for i in range(gap, n):
# # i = [gap, gap+1, gap+2, gap+3... n-1]
# while:
# if alist[i] < alist[i-gap]:
# alist[i], alist[i-gap] = alist[i-gap], alist[i]
# gap变化到0之前，插入算法执行的次数
while gap > 0:
# 插入算法，与普通的插入算法的区别就是gap步长
for j in range(gap, n):
# j = [gap, gap+1, gap+2, gap+3, ..., n-1]
i = j
while i > 0:
if alist[i] < alist[i-gap]:
alist[i], alist[i-gap] = alist[i-gap], alist[i]
i -= gap
else:
break
# 缩短gap步长
gap //= 2
二路归并排序
def merge_sort(alist):
"""归并排序"""
n = len(alist)
if n <= 1:
return alist
mid = n//2
# left 采用归并排序后形成的有序的新的列表
left_li = merge_sort(alist[:mid])
# right 采用归并排序后形成的有序的新的列表
right_li = merge_sort(alist[mid:])
# 将两个有序的子序列合并为一个新的整体
# merge(left, right)
left_pointer, right_pointer = 0, 0
result = []
while left_pointer < len(left_li) and right_pointer < len(right_li):
if left_li[left_pointer] <= right_li[right_pointer]:
result.append(left_li[left_pointer])
left_pointer += 1
else:
result.append(right_li[right_pointer])
right_pointer += 1
result += left_li[left_pointer:]
result += right_li[right_pointer:]
return result
快速排序
def quick_sort(alist, first, last):
"""快速排序"""
if first >= last:
return
mid_value = alist[first]
low = first
high = last
while low < high:
# high 左移
while low < high and alist[high] >= mid_value:
high -= 1
alist[low] = alist[high]
while low <high and alist[low] < mid_value:
low += 1
alist[high] = alist[low]
# 从循环退出时，low==high
alist[low] = mid_value
# 对low左边的列表执行快速排序
quick_sort(alist, first, low-1)
# 对low右边的列表排序
quick_sort(alist, low+1, last)
二分查找
- 非递归实现：
def binary_search_2(alist, item):
"""二分查找， 非递归"""
n = len(alist)
first = 0
last = n-1
while first <= last:
mid = (first + last)//2
if alist[mid] == item:
return True
elif item < alist[mid]:
last = mid - 1
else:
first = mid + 1
return False
- 递归实现
def binary_search(alist, item):
"""二分查找,递归"""
n = len(alist)
if n > 0:
mid = n//2
if alist[mid] == item:
return True
elif item < alist[mid]:
return binary_search(alist[:mid], item)
else:
return binary_search(alist[mid+1:], item)
return False