Solve Sudoku

[shreyanshumalviya]

I would like to add code to solve sudoku using Backtracking with java language.
Input:
grid[][] =
[[3 0 6 5 0 8 4 0 0],
[5 2 0 0 0 0 0 0 0],
[0 8 7 0 0 0 0 3 1 ],
[0 0 3 0 1 0 0 8 0],
[9 0 0 8 6 3 0 0 5],
[0 5 0 0 9 0 6 0 0],
[1 3 0 0 0 0 2 5 0],
[0 0 0 0 0 0 0 7 4],
[0 0 5 2 0 6 3 0 0]]
Output:
3 1 6 5 7 8 4 9 2
5 2 9 1 3 4 7 6 8
4 8 7 6 2 9 5 3 1
2 6 3 4 1 5 9 8 7
9 7 4 8 6 3 1 2 5
8 5 1 7 9 2 6 4 3
1 3 8 9 4 7 2 5 6
6 9 2 3 5 1 8 7 4
7 4 5 2 8 6 3 1 9

[shreyanshumalviya]

Generated Pull Request #96, Added problem statement and solution code.