A sum rectangle is a rectangle divided into a grid of unit squares.
Each square contains a number, and the numbers in neighboring squares always satisfy the following property:
The number in any square S that is neither in the bottom row nor in the right column
can be computed as the sum of the following three numbers:
 The number in the square directly below S.
 The number in the square directly to the right of S.
 The number in the other square adjacent to the previous two squares (the one diagonally down and to the right of S).
An example of a correctly filled sum rectangle:
++++++
 88  57  33  10  5 
++++++
 18  13  11  12  7 
++++++
 1  4  2  1  18 
++++++
For example, in the top left corner we have 88 = 18 + 57 + 13.
We have a secret sum rectangle.
You will be given a int[] leftColumn containing the leftmost number in each row of our rectangle, from the top to the bottom.
You will also be given an int[] topRow containing the topmost number in each column of our rectangle, from the left to the right.
Compute and return the number in the bottom right corner. If the input is such that this number cannot be determined uniquely, return 0 instead.
