add 3224

Author: fishercoder1534

Diff for: paginated_contents/algorithms/4th_thousand/README.md

@@ -1,5 +1,6 @@
 | #    | Title                                                                                                                                                               | Solutions                                                                                                                         | Video                                                                         | Difficulty | Tag                                                                  
 |------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|------------|----------------------------------------------------------------------
+| 3224 | [Minimum Array Changes to Make Differences Equal](https://leetcode.com/problems/minimum-array-changes-to-make-differences-equal/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3224.java) |                                                                               | Medium     |
 | 3223 | [Minimum Length of String After Operations](https://leetcode.com/problems/minimum-length-of-string-after-operations/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3223.java) |                                                                               | Medium     |
 | 3222 | [Find the Winning Player in Coin Game](https://leetcode.com/problems/find-the-winning-player-in-coin-game/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3222.java) |                                                                               | Easy       | 
 | 3219 | [Minimum Cost for Cutting Cake II](https://leetcode.com/problems/minimum-cost-for-cutting-cake-ii/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3219.java) |                                                                               | Hard       | Greedy

Diff for: src/main/java/com/fishercoder/solutions/fourththousand/_3224.java

@@ -0,0 +1,68 @@
+package com.fishercoder.solutions.fourththousand;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class _3224 {
+    public static class Solution1 {
+        /**
+         * My completely original solution during the contest.
+         */
+        public int minChanges(int[] nums, int k) {
+            //compute the frequency of each diff
+            Map<Integer, Integer> map = new HashMap<>();
+            for (int i = 0; i < nums.length / 2; i++) {
+                int diff = Math.abs(nums[nums.length - i - 1] - nums[i]);
+                map.put(diff, map.getOrDefault(diff, 0) + 1);
+            }
+            List<int[]> list = new ArrayList<>();
+            for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
+                list.add(new int[]{entry.getKey(), entry.getValue()});
+            }
+            //sort them by their frequency
+            Collections.sort(list, (a, b) -> b[1] - a[1]);
+            List<int[]> modes = new ArrayList<>();
+            modes.add(list.get(0));
+            int i = 1;
+            //in case there are ties for the same mode
+            while (i < list.size() && list.get(i)[1] == list.get(0)[1]) {
+                modes.add(list.get(i++));
+            }
+            //we'll take the second most frequent mode as well, otherwise, test case 4 won't pass
+            if (i < list.size()) {
+                modes.add(list.get(i));
+            }
+            int minChanges = nums.length;
+            for (int[] mode : modes) {
+                minChanges = Math.min(minChanges, computeChanges(mode[0], nums, k));
+            }
+            return minChanges;
+        }
+
+        private int computeChanges(int mode, int[] nums, int k) {
+            int changes = 0;
+            for (int i = 0; i < nums.length / 2; i++) {
+                int diff = Math.abs(nums[nums.length - i - 1] - nums[i]);
+                if (diff != mode) {
+                    if (nums[nums.length - i - 1] > nums[i]) {
+                        if (k - nums[i] >= mode || nums[nums.length - i - 1] >= mode) {
+                            changes++;
+                        } else {
+                            changes += 2;
+                        }
+                    } else {
+                        if (k - nums[nums.length - i - 1] >= mode || nums[i] >= mode) {
+                            changes++;
+                        } else {
+                            changes += 2;
+                        }
+                    }
+                }
+            }
+            return changes;
+        }
+    }
+}

Diff for: src/test/java/com/fishercoder/fourththousand/_3224Test.java

@@ -0,0 +1,37 @@
+package com.fishercoder.fourththousand;
+
+import com.fishercoder.solutions.fourththousand._3224;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class _3224Test {
+    private static _3224.Solution1 solution1;
+
+    @BeforeEach
+    public void setup() {
+        solution1 = new _3224.Solution1();
+    }
+
+
+    @Test
+    public void test1() {
+        assertEquals(2, solution1.minChanges(new int[]{1, 0, 1, 2, 4, 3}, 4));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(2, solution1.minChanges(new int[]{18, 10, 14, 18, 17, 2, 11, 5}, 19));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(4, solution1.minChanges(new int[]{9, 2, 7, 7, 8, 9, 1, 5, 1, 9, 4, 9, 4, 7}, 9));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(7, solution1.minChanges(new int[]{1, 1, 1, 1, 0, 0, 0, 5, 4, 3, 19, 17, 16, 15, 15, 15, 19, 19, 19, 19}, 20));
+    }
+}