'''Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?'''


def single_number(input_array):
	for num in input_array:
		

	return rev_string

def main():
    input_array = [3,4,3,2,2,4,1,5,1]
    print single_number(input_array)

if __name__ == "__main__": main()