Python Program to Sort an array of 0s, 1s and 2s

Given an array A[] consisting 0s, 1s and 2s. The task is to write a function that sorts the given array. The functions should put all 0s first, then all 1s and all 2s in last.

Examples:

Input : {0, 1, 2, 0, 1, 2, 2, 2, 2, 1}
Output : {0, 0, 1, 1, 1, 2, 2, 2, 2, 2}

Input :  {0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1}
Output :  {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2}

Simple Solution : We create three empty lists. We add all 0s to first list, 1s to second list and 2s to third list. Finally we append all lists and return

# Function for sort
def SortWithoutSorting(arr):
# 3 Empty list for initialize 0 1 and 2

    l1 =[]
    l2 =[]
    l3 =[]
    for i in range(len(arr)):
        if arr[i] == 0:
            l1.append(arr[i])
        elif arr[i] == 1:
            l2.append(arr[i])
        else:
            l3.append(arr[i])
    return (l1 + l2 + l3)

# Driver Code
arr = array.array('i', [0, 1, 0, 1, 2, 2, 0, 1])
print(SortWithoutSorting(arr))

Efficient Solution The above solution requires extra space. How to do it without extra space (in-place) in the same given list and using only one traversal. Please refer Sort an array of 0s, 1s and 2s for implementation of the efficient solution.