Method nQueens

java/Backtracking/NQueens.java:7–10

(int n)

    int res = 0;

    public int nQueens(int n) {
        dfs(0, new HashSet<>(), new HashSet<>(), new HashSet<>(), n);
        return res;
    }

    private void dfs(int r, Set<Integer> diagonalsSet, Set<Integer> antiDiagonalsSet, Set<Integer> colsSet, int n) {
        // Termination condition: If we have reached the end of the rows,