add permutation

Author: genkimaru

pom.xml

@@ -13,4 +13,12 @@
         <maven.compiler.target>22</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>RELEASE</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
 </project>

src/main/java/com/leetcode/Arrangement.java

@@ -0,0 +1,73 @@
+package com.leetcode;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.function.Consumer;
+
+/**
+ * permutation or  arrangement problem: [1,2,3] => [1,2,3] [1,3,2] ,[2,1,3] ,[2,3,1],[3,1,2],[3,2,1]
+ */
+public class Arrangement {
+
+    private int count;
+    private ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
+    private HashMap<Integer, Integer> map = new HashMap<>();
+
+    public void arrange(int[] arr) {
+
+        if (arr.length > 2) {
+            for (int ele : arr) {
+                map.put(arr.length - 1, ele);
+                arrange(restOfArr(ele, arr));
+            }
+        } else if (arr.length == 2) {
+//            System.out.println(arr[0] + " , " + arr[1]);
+//            System.out.println(arr[1] + " , " + arr[0]);
+            map.put(1, arr[1]);
+            map.put(0, arr[0]);
+            ArrayList<Integer> list = new ArrayList<>();
+            for (int i = map.size() - 1; i >= 0; i--) {
+                list.add(map.get(i));
+            }
+            result.add(list);
+            map.put(1, arr[0]);
+            map.put(0, arr[1]);
+            ArrayList<Integer> list2 = new ArrayList<>();
+            for (int i = map.size() - 1; i >= 0; i--) {
+                list2.add(map.get(i));
+            }
+            result.add(list2);
+            count++;
+            count++;
+        }
+    }
+
+    protected int[] restOfArr(int ele, int[] arr) {
+        int[] rest = new int[arr.length - 1];
+        int i = 0;
+        for (int e : arr) {
+            if (ele == e) {
+                continue;
+            }
+            rest[i] = e;
+            i++;
+        }
+        return rest;
+    }
+
+    public static void main(String[] args) {
+        int[] arr = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
+        Arrangement arrangement = new Arrangement();
+        arrangement.arrange(arr);
+        arrangement.result.stream().forEach(new Consumer<ArrayList<Integer>>() {
+            @Override
+            public void accept(ArrayList<Integer> integers) {
+                for (int i : integers) {
+                    System.out.print(i + ", ");
+                }
+                System.out.println();
+            }
+        });
+        System.out.println(arrangement.count);
+    }
+}

src/test/java/com/leetcode/ArrangementTest.java

@@ -0,0 +1,17 @@
+package com.leetcode;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+
+class ArrangementTest {
+
+    @Test
+    public void restOfArrTest(){
+        int[] arr = new int[]{1,2,3,4,5,6};
+        int[] restOfArr = new Arrangement().restOfArr(1, arr);
+        Assertions.assertArrayEquals(new int[]{2,3,4,5,6} , restOfArr);
+    }
+
+
+}