Java - 순열, 조합

public class Main {

    public static void main(String[] args) {
        int n = 10, r = 5;
        int[] ret = new int[r];
        System.out.println(n + "C" + r);
        combi(ret, n, r, 0, 0);

        System.out.println("\n"+n + "P" + r);
        boolean[] visited = new boolean[n];
        ret = new int[r];
        perm(ret, visited, 0, n, r);

    }

    //nCr
    static void combi(int[] ret, int n, int r, int index, int target) {
        if (r == 0) {
            for (int i : ret) {
                System.out.print(i + " ");
            }
            System.out.println();
            return;
        }
        if (target == n) return;

        ret[index] = target;
        combi(ret, n, r - 1, index + 1, target + 1);  //뽑는 경우
        combi(ret, n, r, index, target + 1);  //안뽑는 경우
    }

    /* 중복 조합
       combi(ret, n, r - 1, index + 1, target + 1);
    -> combi(ret, n, r - 1, index + 1, target);
    * */

    //nPr
    static void perm(int[] ret, boolean[] visited, int depth, int n, int r) {
        if (depth == r) {
            for (int i : ret) {
                System.out.print(i + " ");
            }
            System.out.println();
            return;
        }

        for (int i = 0; i < n; i++) {
            if (visited[i]) continue;

            visited[i] = true;
            ret[depth] = i;
            perm(ret, visited, depth + 1, n, r);
            visited[i] = false;
        }
    }

    /*중복 순열
      visited 부분 제거
     */

}