Method totalNQueens

java/0052-n-queens-ii.java:4–10

(int n)

    int count = 0;

    public int totalNQueens(int n) {
        Set<Integer> colSet = new HashSet<>();
        Set<Integer> posDiagSet = new HashSet<>(); // (r + c)
        Set<Integer> negDiagSet = new HashSet<>(); // (r - c)
        backtrack(0, n, colSet, posDiagSet, negDiagSet);
        return count;
    }

    private void backtrack(
            int row,