快速排序
def partition(li, left, right):
tmp = li[left]
while left < right:
while left < right and li[right] >= tmp: #从右面找比tmp小的数
right -= 1 # 往左走一步
li[left] = li[right] #把右边的值写到左边空位上
# print(li, 'right')
while left < right and li[left] <= tmp:
left += 1
li[right] = li[left] #把左边的值写到右边空位上
# print(li, 'left')
li[left] = tmp # 把tmp归位
return left
def _quick_sort(li, left, right):
if left<right: # 至少两个元素
mid = partition(li, left, right)
_quick_sort(li, left, mid-1)
_quick_sort(li, mid+1, right)
def quick_sort(li):
_quick_sort(li, 0, len(li)-1)
堆排序
def sift(li, low, high):
"""
:param li: 列表
:param low: 堆的根节点位置
:param high: 堆的最后一个元素的位置
:return:
"""
i = low # i最开始指向根节点
j = 2 * i + 1 # j开始是左孩子
tmp = li[low] # 把堆顶存起来
while j <= high: # 只要j位置有数
if j + 1 <= high and li[j+1] > li[j]: # 如果右孩子有并且比较大
j = j + 1 # j指向右孩子
if li[j] > tmp:
li[i] = li[j]
i = j # 往下看一层
j = 2 * i + 1
else: # tmp更大，把tmp放到i的位置上
li[i] = tmp # 把tmp放到某一级领导位置上
break
else:
li[i] = tmp # 把tmp放到叶子节点上
def heap_sort(li):
n = len(li)
for i in range((n-2)//2, -1, -1):
# i表示建堆的时候调整的部分的根的下标
sift(li, i, n-1)
# 建堆完成了
for i in range(n-1, -1, -1):
# i 指向当前堆的最后一个元素
li[0], li[i] = li[i], li[0]
sift(li, 0, i - 1) #i-1是新的high
# python自带堆排序算法
heapq.heapify(li) #建堆
n=len(li)
for i in range(n):
print(heapq.heappop(li), end=',')
# 堆排序的应用，取列表前k个大的数
def sift(li, low, high):
i = low
j = 2 * i + 1
tmp = li[low]
while j <= high:
if j + 1 <= high and li[j+1] < li[j]:
j = j + 1
if li[j] < tmp:
li[i] = li[j]
i = j
j = 2 * i + 1
else:
break
li[i] = tmp
def topk(li, k):
heap = li[0:k]
for i in range((k-2)//2, -1, -1):
sift(heap, i, k-1)
# 1.建堆
for i in range(k, len(li)-1):
if li[i] > heap[0]:
heap[0] = li[i]
sift(heap, 0, k-1)
# 2.遍历
for i in range(k-1, -1, -1):
heap[0], heap[i] = heap[i], heap[0]
sift(heap, 0, i - 1)
# 3.出数
return heap
归并排序
def merge(li, low, mid, high):
i = low
j = mid + 1
ltmp = []
while i<=mid and j<=high: # 只要左右两边都有数
if li[i] < li[j]:
ltmp.append(li[i])
i += 1
else:
ltmp.append(li[j])
j += 1
# while执行完，肯定有一部分没数了
while i <= mid:
ltmp.append(li[i])
i += 1
while j <= high:
ltmp.append(li[j])
j += 1
li[low:high+1] = ltmp
def merge_sort(li, low, high):
if low < high: #至少有两个元素，递归
mid = (low + high) //2
merge_sort(li, low, mid)
merge_sort(li, mid+1, high)
merge(li, low, mid, high)
