solves find all numbers in an array

Author: anishLearnsToCode

README.md

@@ -117,7 +117,7 @@
 | 441 | [Arranging Coins](https://leetcode.com/problems/arranging-coins) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/ArrangingCoins.java) |
 | 443 | [String Compression](https://leetcode.com/problems/string-compression) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/StringCompression.java) |
 | 447 | [Number of Boomerangs](https://leetcode.com/problems/number-of-boomerangs) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/NumberOfBoomerangs.java) |
-| 448 | [Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array) | Easy | |
+| 448 | [Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](src/FindAllNumbersDisappearedInAnArray.java) |
 | 453 | [Minimum Moves to Equal Array Elements](https://leetcode.com/problems/minimum-moves-to-equal-array-elements) | Easy | |
 | 455 | [Assign Cookies](https://leetcode.com/problems/assign-cookies) | Easy | |
 | 459 | [Repeated Substring Pattern](https://leetcode.com/problems/repeated-substring-pattern) | Easy | |

src/FindAllNumbersDisappearedInAnArray.java

@@ -0,0 +1,28 @@
+// Problem Number: 448
+// https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public class FindAllNumbersDisappearedInAnArray {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        Set<Integer> numbers = uniqueNumbersFrom(nums);
+        List<Integer> result = new ArrayList<>();
+        for (int i = 1 ; i <= nums.length ; i++) {
+            if (!numbers.contains(i)) {
+                result.add(i);
+            }
+        }
+        return result;
+    }
+
+    private Set<Integer> uniqueNumbersFrom(int[] array) {
+        Set<Integer> result = new HashSet<>();
+        for (int number : array) {
+            result.add(number);
+        }
+        return result;
+    }
+}