add 2784

Author: fishercoder1534

Diff for: paginated_contents/algorithms/3rd_thousand/README.md

@@ -10,6 +10,7 @@
 | 2824 | [Count Pairs Whose Sum is Less than Target](https://leetcode.com/problems/count-pairs-whose-sum-is-less-than-target/)                                                                                                          | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2824.java)                                       |                                      | Easy                           |
 | 2812 | [Find the Safest Path in a Grid](https://leetcode.com/problems/find-the-safest-path-in-a-grid/)                                                                                                             | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2812.java)                                       |                                      | Medium                         |BFS
 | 2810 | [Faulty Keyboard](https://leetcode.com/problems/faulty-keyboard/)                                                                                                              | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2810.java)                                       |                                      | Easy                           |
+| 2784 | [Check if Array is Good](https://leetcode.com/problems/check-if-array-is-good/)                                                                                                            | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2784.java)                                       |                                      | Easy                           |
 | 2778 | [Sum of Squares of Special Elements](https://leetcode.com/problems/sum-of-squares-of-special-elements/)                                                                                                            | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2778.java)                                       |                                      | Easy                           |
 | 2769 | [Find the Maximum Achievable Number](https://leetcode.com/problems/find-the-maximum-achievable-number/)                                                                                                            | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2769.java)                                       |                                      | Easy                           |
 | 2765 | [Longest Alternating Subarray](https://leetcode.com/problems/longest-alternating-subarray/)                                                                                                             | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2765.java)                                       |                                      | Easy                           |

Diff for: src/main/java/com/fishercoder/solutions/thirdthousand/_2784.java

@@ -0,0 +1,27 @@
+package com.fishercoder.solutions.thirdthousand;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class _2784 {
+    public static class Solution1 {
+        public boolean isGood(int[] nums) {
+            int max = -1;
+            for (int i = 0; i < nums.length; i++) {
+                max = Math.max(max, nums[i]);
+            }
+            if (nums.length != max + 1) {
+                return false;
+            }
+            Set<Integer> set = new HashSet<>();
+            for (int num : nums) {
+                if (!set.add(num)) {
+                    if (num != max) {
+                        return false;
+                    }
+                }
+            }
+            return set.size() == max;
+        }
+    }
+}