找中位数（快排法）

array=[5,40,2,4,55,6]
def qsort(array,left,right):
    if(left>=right):
        return array
    lp=left
    rp=right
    key=array[left]
    while lp<rp:
        while (array[rp] >= key) and (lp < rp):
            rp -= 1
        while (array[lp]<=key) and (lp<rp):
            lp+=1
        array[lp],array[rp]=array[rp],array[lp]
    array[lp],array[left]=array[left],array[lp]
    qsort(array,left,lp-1)
    qsort(array,rp+1,right)
    print(array)
    return array
def quick_sort(array):
    return qsort(array,0,len(array)-1)

a=quick_sort(array)
# 偶数
if(len(array)%2==0):
    print((a[len(array)//2-1]+a[len(array)//2])/2)
else:
    print(a[len(array)//2])