bokmann/the_daycare.txt

## the_daycare.txt
Problem A The Daycare
The daycare Nannies R Us has installed a new high-tech system for keeping track of which children are under
its supervision at any moment in time. Each parent of a child has a card with a unique ID, where the ID is
some integer x. Every morning, the parent swipes the card at a card-reader when dropping their child off at
the daycare. The system then adds x to an array of integers. In the evening, when the parent comes to pick
up the child, the same card is swiped, and a second copy of x is added to the list. Each night at midnight,
the array is wiped clean and reset to have zero elements. In this way, the daycare can quickly check every
afternoon which children are yet to be picked up by their parents by picking out the array elements that
occur precisely once. Unfortunately, at 4:55 pm on Friday, March 13, 2015, the daycare realizes that
somewhere in their daycare is precisely one child who is yet to be picked up – can you help them determine
the integer ID of this child?

Input
The input consists of two rows. On the first row, an integer n satisfying 1<= n <= 10,000 is given. On the
second row, a sequence of n integers is given.

Output
The ID of the child left in the daycare.

Sample Inputs
7
1 1 2 9 -11 -11 9

9
1 2 1 3 2 4 3 4 5


Sample Outputs
2 5
	Problem A The Daycare
	The daycare Nannies R Us has installed a new high-tech system for keeping track of which children are under
	its supervision at any moment in time. Each parent of a child has a card with a unique ID, where the ID is
	some integer x. Every morning, the parent swipes the card at a card-reader when dropping their child off at
	the daycare. The system then adds x to an array of integers. In the evening, when the parent comes to pick
	up the child, the same card is swiped, and a second copy of x is added to the list. Each night at midnight,
	the array is wiped clean and reset to have zero elements. In this way, the daycare can quickly check every
	afternoon which children are yet to be picked up by their parents by picking out the array elements that
	occur precisely once. Unfortunately, at 4:55 pm on Friday, March 13, 2015, the daycare realizes that
	somewhere in their daycare is precisely one child who is yet to be picked up – can you help them determine
	the integer ID of this child?

	Input
	The input consists of two rows. On the first row, an integer n satisfying 1<= n <= 10,000 is given. On the
	second row, a sequence of n integers is given.

	Output
	The ID of the child left in the daycare.

	Sample Inputs
	7
	1 1 2 9 -11 -11 9

	9
	1 2 1 3 2 4 3 4 5







	Sample Outputs
	2 5