NQueen Succint Java Solution

Nqueen.java

class Solution {

    private static final String DOT = ".";
    private static final String Q = "Q";

    public static void main(String[] args) {
        var soln = new Solution().solveNQueens(8);
        for (var s : soln) {
            for (var r : s) {
                System.out.println(r);
            }
            System.out.println();
            System.out.println();
        }
    }

    public List<List<String>> solveNQueens(int n) {
        List<List<Integer>> results = new ArrayList<>();
        generateSolutions(n, 0, new ArrayList<>(), results);
        return results.stream().map(this::stringify).collect(Collectors.toList());
    }

    private void generateSolutions(int n, int i, List<Integer> slate, List<List<Integer>> results) {
        if (i == n) {
            results.add(new ArrayList<>(slate));
            return;
        }
        for (int j=0; j<n; j++) {
            if (!isAttack(slate, j)) {
                slate.add(j);
                generateSolutions(n, i + 1, slate, results);
                slate.remove(slate.size() - 1);
            }
        }
    }
    private boolean isAttack(List<Integer> slate, int n) {
        int newPos = slate.size();
        for (int i = 0; i<slate.size(); i++) {
            if (slate.get(i) == n || Math.abs(slate.get(i) - n) == (newPos - i)) {
                return true;
            }
        }
        return false;
    }

    public List<String> stringify(List<Integer> result) {
        List<String> list_strings = new ArrayList<>();
        int n = result.size();
        for (int r : result) {
            StringBuilder sb = new StringBuilder();
            sb.append(DOT.repeat(r)).append(Q).append(DOT.repeat(n-r-1));
            list_strings.add(sb.toString());
        }
        return list_strings;
    }
}