@@ -0,0 +1,60 @@
+import java.util.ArrayList;
+
+public class CombinationPermutation {
+    public static void main(String[] args) {
+
+        String s = "abcd";
+        int k = 2;
+        System.out.println("Combination");
+        combinationK("", s, k);
+        System.out.println("Permutation");
+        permutationK(s.toCharArray(), s.length(), k);
+        System.out.println("MoveInOut");
+        move(s.toCharArray(), s.length(), new ArrayList<String>(), true);
+
+    }
+
+    public static void combinationK(String prefix, String s, int K) {
+        if (K == 0) {
+            System.out.println(prefix);
+            return;
+        }
+        for (int i = 0; i < s.length(); ++i)
+            combinationK(prefix + s.charAt(i), s.substring(i + 1), K - 1);
+    }
+
+    public static void permutationK(char[] s, int n, int K) {
+        if (K == 0) {
+            for (int i = n; i < s.length; ++i)
+                System.out.print(s[i]);
+            System.out.println();
+            return;
+        }
+        for (int i = 0; i < n; ++i) {
+            swap(s, i, n - 1);
+            permutationK(s, n - 1, K - 1);
+            swap(s, i, n - 1);
+        }
+    }
+
+    public static void swap(char[] a, int left, int right) {
+        char tmp = a[left];
+        a[left] = a[right];
+        a[right] = tmp;
+    }
+
+    public static void move(char[] s, int n, ArrayList<String> result, boolean pick) {
+        if (n == 0) {
+            System.out.println(result.toString());
+            return;
+        }
+        move(s, n - 1, result, true);
+        if (pick) {
+            result.add(String.valueOf(s[n - 1]));
+        } else {
+            result.remove(String.valueOf(s[n - 1]));
+        }
+        move(s, n - 1, result, false);
+
+    }
+}
@@ -58,7 +58,7 @@ public static void main(String[] args) {
         int N = Integer.parseInt(s.nextLine());
         String alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
         String elements = alphabet.substring(0, N);
-        // perm1(elements);
+        perm1(elements);
         System.out.println();
         perm2(elements);
     }
Original file line number	Diff line number	Diff line change
`@@ -58,7 +58,7 @@ public static void main(String[] args) {`
`58`	`58`	`int N = Integer.parseInt(s.nextLine());`
`59`	`59`	`String alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";`
`60`	`60`	`String elements = alphabet.substring(0, N);`
`61`		`- // perm1(elements);`
	`61`	`+ perm1(elements);`
`62`	`62`	`System.out.println();`
`63`	`63`	`perm2(elements);`
`64`	`64`	`}`