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常见排序算法效率

冒泡排序

def bubble_sort(alist):
    """冒泡排序"""
    n = len(alist)
    for j in range(n-1):
        count = 0
        for i in range(0, n-1-j):
            # 班长从头走到尾
            if alist[i] > alist[i+1]:
                alist[i],alist[i+1] = alist[i+1], alist[i]
                count += 1
        if 0 == count:
            return


# [1, 2,3 ,4 ,5, 6]



# i 0 ~ n-2   range(0, n-1) j=0
# i 0 ~ n-3   range(0, n-1-1) j=1
# i 0 ~ n-4   range(0, n-1-2) j=2
# j=n  i  range(0, n-1-j)
if __name__ == "__main__":
    li = [54, 26, 93, 17, 77, 31, 44, 55, 20]
    print(li)
    bubble_sort(li)
    print(li)

# for j in range(len(alist)-1,0,-1)
#
# [n-1, n-2, n-3, n-4,..., 1]
# for i in range(j)
#
# [0, 1, 2, 3,...,n-2]
# for i in range(n-1-j)

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)


if __name__ == "__main__":
    li = [54, 26, 93, 17, 77, 31, 44, 55, 20]
    print(li)
    quick_sort(li, 0, len(li)-1)
    print(li)
    ```
    # 二分查找法
    # [17, 20, 26, 31, 44, 54, 55, 77, 93]
# mid = n/2
#
# [17, 20, 26, 31]
# mid = n/2

二分查找法

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



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






if __name__ == "__main__":
    li = [17, 20, 26, 31, 44, 54, 55, 77, 93]
    print(binary_search(li, 55))
    print(binary_search(li, 100))
    print(binary_search_2(li, 55))
    print(binary_search_2(li, 100))

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