sort-array-by-parity.py

# Time:  O(n)
# Space: O(1)

# Given an array A of non-negative integers,
# return an array consisting of all the even elements of A,
# followed by all the odd elements of A.
#
# You may return any answer array that satisfies this condition.
#
# Example 1:
#
# Input: [3,1,2,4]
# Output: [2,4,3,1]
# The outputs [4,2,3,1], [2,4,1,3], and [4,2,1,3]
# would also be accepted.
#
# Note:
# - 1 <= A.length <= 5000
# - 0 <= A[i] <= 5000

class Solution(object):
    def sortArrayByParity(self, A):
        """
        :type A: List[int]
        :rtype: List[int]
        """
        i = 0
        for j in xrange(len(A)):
            if A[j] % 2 == 0:
                A[i], A[j] = A[j], A[i]
                i += 1
        return A