quicksort--python--others

搜了stackoverflow 上的quicksort, 明白了什么叫elegant, compact code:

def qsort(arr): 
     if len(arr) <= 1:
          return arr
     else:
          return qsort([x for x in arr[1:] if x<arr[0]]) + [arr[0]] + qsort([x for x in arr[1:] if x>=arr[0]])

Or you can make this a little bit longer to make sense:

def sort(array=[12,4,5,6,7,3,1,15]):
    less = []
    equal = []
    greater = []

    if len(array) > 1:
        pivot = array[0]
        for x in array:
            if x < pivot:
                less.append(x)
            if x == pivot:
                equal.append(x)
            if x > pivot:
                greater.append(x)

        # Don't forget to return something!
        return sort(less)+ equal +sort(greater)  # Just use the + operator to join lists
    # Note that you want equal ^^^^^ not pivot
    else:  # You need to hande the part at the end of the recursion - when you only have one element in your array, just return the array.
        return array

or this version:

def sort(A):
    if len(A) <= 1:
        return A
    else:
        pivot = A[0]
        
        small = []
        mid = []
        big = []

        for item in A:
            if item == pivot:
                mid.append(item)
            elif item > pivot:
                big.append(item)
            else:
                small.append(item)
        small = sort(small)
        mid = mid  #不能递归sort(mid)，否则当有重复元素时，会死循环
        big = sort(big)
        A = small + mid + big
        return A
A = [10,10,11,52,3,8,4,-1]

print A
print sort(A)