```
class Solution:
# @param A a list of integers
# @return nothing, sort in place
def sortColors(self, A):
if len(A) < 2:
return
start, left, right, end = 0, 0, len(A), len(A)
while left < right:
if A[left] == 1:
left += 1
elif A[right-1] == 1:
right -= 1
elif A[left] == 0:
A[start], A[left] = A[left], A[start]
left += 1
start += 1
elif A[right-1] == 2:
A[right-1], A[end-1] = A[end-1], A[right-1]
right -= 1
end -= 1
else:
A[left], A[right-1] = A[right-1], A[left]
```