move-zeroes.py

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

# Given an array nums, write a function to move all 0's
# to the end of it while maintaining the relative order 
# of the non-zero elements.
#
# For example, given nums = [0, 1, 0, 3, 12], after 
# calling your function, nums should be [1, 3, 12, 0, 0].
#
# Note:
# You must do this in-place without making a copy of the array.
# Minimize the total number of operations.


class Solution(object):
    def moveZeroes(self, nums):
        """
        :type nums: List[int]
        :rtype: void Do not return anything, modify nums in-place instead.
        """
        pos = 0
        for i in xrange(len(nums)):
            if nums[i]:
                nums[i], nums[pos] = nums[pos], nums[i]
                pos += 1

    def moveZeroes2(self, nums):
        """
        :type nums: List[int]
        :rtype: void Do not return anything, modify nums in-place instead.
        """
        nums.sort(cmp=lambda a, b: 0 if b else -1)


class Solution2(object):
    def moveZeroes(self, nums):
        """
        :type nums: List[int]
        :rtype: void Do not return anything, modify nums in-place instead.
        """
        pos = 0
        for i in xrange(len(nums)):
            if nums[i]:
                nums[pos] = nums[i]
                pos += 1
        
        for i in xrange(pos, len(nums)):
            nums[i] = 0 


if __name__ == '__main__':
    s = Solution()
    r = s.moveZeroes([0, 1, 0, 3, 12])
    print r