update

Author: yennj12

leetcode_java/src/main/java/dev/Sorting/ArraySortTest.java

@@ -1,4 +1,59 @@
 package dev.Sorting;
 
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
+
 public class ArraySortTest {
+
+    @Test
+    public void testOnArrayVal1(){
+
+        Integer[] arr = new Integer[5];
+        arr[0] = 10;
+        arr[1] = -1;
+        arr[2] = 99;
+        arr[3] = 7;
+        arr[4] = 2;
+
+        /** NOTE !!! how we print context inside array
+         *
+         *   -> via Arrays.asList()
+         */
+        System.out.println(">>> (before) arr = " + Arrays.asList(arr));
+
+        /**
+         *  NOTE !!!
+         *
+         *   instead of `Collections.sort`, we use Arrays.sort
+         */
+        // V1: Comparator.compare
+        Arrays.sort(arr, new Comparator<Integer>(){
+            @Override
+            public int compare(Integer o1, Integer o2) {
+                int diff = o2 - o2;
+                return diff;
+            }
+        });
+
+        // V2: lambda
+//        Arrays.sort(arr, (x, y) ->{
+//            int diff = y - x;
+//            return diff;
+//        });
+
+
+        // NOTE !!! below is WRONG
+
+//        Collections.sort(arr,  new Comparator<Integer>(){
+//            @Override
+//            public int compare(Integer o1, Integer o2) {
+//                return 0;
+//            }
+//        });
+
+        System.out.println(">>> (after) arr = " + Arrays.asList(arr));
+    }
 }

leetcode_java/src/main/java/dev/Sorting/ListSortTest.java

@@ -16,26 +16,34 @@ public void testSortListWithVal_1(){
         list.add(-3);
 
         System.out.println(">>> (before) list = " + list);
-        
+
         // V1: lambda
-        Collections.sort(list, (x,y) -> {
-            int diff = y - x;
-            return diff;
-        });
-//
-//        // V2: Comparator.compare
-//        Collections.sort(list, new Comparator<Integer>(){
-//            @Override
-//            public int compare(Integer o1, Integer o2) {
-//                //int diff = o1 - o2;  // smaller first (increasing order)
-//                int diff = o2 - o1; // bigger first, (decreasing order)
-////                if(diff == 0){
-////                    return
-////                }
-//                return diff;
-//            }
+//        Collections.sort(list, (x,y) -> {
+//            int diff = y - x;
+//            return diff;
 //        });
 
+        // V2: Comparator.compare
+        /**
+         * NOTE !!!
+         *
+         *
+         *  need to offer TYPE for comparator
+         *
+         *  e.g. `new Comparator<Integer>()`
+         */
+        Collections.sort(list, new Comparator<Integer>(){
+            @Override
+            public int compare(Integer o1, Integer o2) {
+                //int diff = o1 - o2;  // smaller first (increasing order)
+                int diff = o2 - o1; // bigger first, (decreasing order)
+//                if(diff == 0){
+//                    return
+//                }
+                return diff;
+            }
+        });
+
         System.out.println(">>> (after) list = " + list);
 
     }