python——算法（冒泡排序，选择排序，分治，顺序查找，二分查找）

2024年1月7日 74次阅读

冒泡排序

def bubbleSort(a):
    for i in range(len(a)-1):
        flag=True
        for j in  range(len(a)-1-i):
            if a[j]>a[j+1]:
                a[j],a[j+1]=a[j+1],a[j]
            flag=False
        if flag:
            break
        print(a)#打印排序过程
def main():
    a=[865,451,239,12,192,180,7,123,44,100]
    bubbleSort(a)
    print("-------------------------------------------------")
    print("最终排序结果：")
    print(a)
if __name__ == '__main__':
    main()

选择排序

def selectionSort(a):
    for i in range(0,len(a)):#外循环0~N-1
        m=i#当前位置下标
        for j in range(i+1,len(a)):#内循环
            if a[j]<a[m]:
                m=j
        a[i],a[m]=a[m],a[i]
def main():
    a=[59,12,77,64,72,69,46,89,31,9]
    selectionSort(a)
    print(a)
if __name__ == '__main__':
    main()

分治

a=[]
k=(int)(input("请输入k值"))
for i in range(k+1):
    s=2**i
    a.append(s)
print(a)
def Comparemax(x,y):
    if x>y:
        max=x
    else:
        max=y
    return max

def Comparemin(x,y):
    if x < y:
        min = x
    else:
        min = y
    return min
def findMax(a,left,right):
    if left==right:
        max=a[right]
        return max
    if right-left==1:
        LM=a[left]
        RM=a[right]
        return (Comparemax(LM,RM))
    if right - left > 1:
        mid=(left+right)//2
        LM=findMax(a,left,mid)
        RM=findMax(a,mid+1,right)
        return (Comparemax(LM,RM))
def findMin(a,left,right):
    if left == right:
        min = a[left]
        return min
    if right - left == 1:
        LM = a[left]
        RM = a[right]
        return (Comparemin(LM, RM))
    if right-left>1:
        mid = (left + right) // 2
        LM = findMin(a, left, mid)
        RM = findMin(a, mid+1, right)
        return (Comparemin(LM, RM))
def main():
    print("最小值：")
    print(findMin(a,0,len(a)-1))
    print("最大值：")
    print(findMax(a, 0, len(a)-1))
if __name__ == '__main__':
    main()

顺序查找

def sequentialSearch(alist,item):#顺序查找
    pos=0#初始查找位置
    found=False#为找打数据对象
    while pos<len(alist)and not found:
        if alist[pos]==item:
            found=True
        else:
            pos=pos+1
    return found,pos

def main():
    testlist=[1,3,33,8,37,29,32,15,5]
    print(sequentialSearch(testlist,3))
    print(sequentialSearch(testlist,15))
if __name__ == '__main__':
    main()

二分查找递归

def _binarySearch(key,a,lo,hi):
    if hi<=lo:return -1
    mid=(lo+hi)//2
    if a[mid]>key:
        return _binarySearch(key,a,lo,mid)
    elif a[mid]<key:
        return _binarySearch(key,a,mid+1,hi)
    else:return mid
def binarySearch(key,a):
    return _binarySearch(key,a,0,len(a))
def main():
    a=[1,13,26,33,45,55,68,72,83,99]
    print("关键字列表索引位于",binarySearch(83,a))
    print("关键字列表索引位于", binarySearch(10, a))
if __name__ == '__main__':
    main()

二分查找非递归

def binarySearch(key,a):
    low=0
    high=len(a)-1
    while low<=high:
        mid=(low+high)//2
        if a[mid]<key:low=mid+1
        elif a[mid]>key:high=mid-1
        else: return mid
    return -1
def main():
    a=[1,34,56,78,98,99.8]
    print("关键字位于列表索引",binarySearch(99.8,a))
    print("关键字位于列表索引", binarySearch(78, a))
    print("关键字位于列表索引", binarySearch(23,a))
main()
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