public List<List<String>> solveNQueens(int n) {
        List<List<String>> result = new ArrayList<>();
        Position[] positions = new Position[n];
        solve(0, positions, result, n);
        return result;
    }
Date 02/20/2016
@author Tushar Roy

Given nxn board place n queen on this board so that they dont attack each other. One solution is to find
any placement of queens which do not attack each other. Other solution is to find all placements of queen
on the board.

Time complexity O(n*n)
Space complexity O(n*n)
src/com/interview/recursion/NQueenProblem.java