Kata

Description

Here is a 4x4 chessboard, each grid put a number. Then, we operate on these numbers: pick any two adjacent grids, the numbers of two grid at the same time +1 or -1... After n times operation, we got a new chessboard with different numbers. One of the numbers is missing, please get it back.

Task

Complete function missingNumber() that accepts two arguments board1 and board2. They are two 2D array that contains some numbers. board1 is the original chessboard, board2 is the chessboard after n times operation. One of the elements of board2 is "?", please return the number of this grid.

Examples

board1=[
[1,1,1,1],
[2,2,2,2],
[3,3,3,3],
[4,4,4,4]
]
board2=[
[1,1,1,1],
[1,2,3,2],
[2,2,"?",4],
[4,3,5,4]
]

missingNumber(board1,board2) ===6

board1=[
[ 1, 2, 3, 4],
[ 5, 6, 7, 8],
[ 9,10,11,12],
[13,14,15,16]
]
board2=[
[ 1, 2, 3, 4],
[ 6, 6, 7, 7],
[20,20,20,20],
[13,14,14,"?"]
]

missingNumber(board1,board2) ===15
board1=[
[ 1, 2, 3, 4],
[ 5, 6, 7, 8],
[ 9,10,11,12],
[13,14,15,16]
]
board2=[
["?",20,20,20],
[20,20,20,20],
[20,20,20,20],
[20,20,20,20]
]

missingNumber(board1,board2) ===20

Hint: 1.The missing number can be positive integers, negative integers and zero; 2.If you have no idea, please think about why the operation only between two adjacent grids. On the chessboard, they always be a white grid and a black grid ;-)