memorandum

Code memorandum

Useful code sample found on the net

Enumeration of all combinations

The source is here Click here for commentary (https://qiita.com/masakinpo/items/b6ae147d9a61b592240a)

·permutation

    public static void permutation(String q, String ans){
        // Base Case
        if(q.length() <= 1) {
            System.out.println(ans + q);
        }
        // General Case
        else {
            for (int i = 0; i < q.length(); i++) {
                permutation(q.substring(0, i) + q.substring(i + 1),
                        ans + q.charAt(i));
            }
        }
    }

・ Combination

    public static void combination(String q, String ans, int k){
        // Base Case
        if(ans.length() == k) {
            System.out.println(ans);
        }
        // General Case
        else {
            while (q.length() > 0) {
                combination(q.substring(1), ans + q.charAt(0), k);
                q = q.substring(1);
            }
        }
    }
    public static void main(String[] args) {
        combination("abcd", "", 2);
    }

-Treat the second argument ans like a private constructor


public static void permutation(String q){
  permutation(q, "");
}

private static void permutation(String q, String ans){
 //省略
}