add 3912

Author: fishercoder1534

paginated_contents/algorithms/4th_thousand/README.md

@@ -19,6 +19,7 @@
 | 3921 | [Score Validator](https://leetcode.com/problems/score-validator/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3921.java) |                                                                               | Easy       |
 | 3917 | [Count Indices With Opposite Parity](https://leetcode.com/problems/count-indices-with-opposite-parity/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3917.java) |                                                                               | Easy       |
 | 3913 | [Sort Vowels by Frequency](https://leetcode.com/problems/sort-vowels-by-frequency/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3913.java) |                                                                               | Easy       |
+| 3912 | [Valid Elements in an Array](https://leetcode.com/problems/valid-elements-in-an-array/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3912.java) |                                                                               | Easy       |
 | 3908 | [Valid Digit Number](https://leetcode.com/problems/valid-digit-number/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3908.java) |                                                                               | Easy       |
 | 3701 | [Compute Alternating Sum](https://leetcode.com/problems/compute-alternating-sum/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3701.java) |                                                                               | Easy       |
 | 3662 | [Filter Characters by Frequency](https://leetcode.com/problems/filter-characters-by-frequency/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3662.java) |                                                                               | Easy       |

src/main/java/com/fishercoder/solutions/fourththousand/_3912.java

@@ -0,0 +1,35 @@
+package com.fishercoder.solutions.fourththousand;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class _3912 {
+    public static class Solution1 {
+        public List<Integer> findValidElements(int[] nums) {
+            boolean[] valid = new boolean[nums.length];
+            valid[0] = true;
+            valid[nums.length - 1] = true;
+            int leftMax = nums[0];
+            for (int i = 1; i < nums.length; i++) {
+                if (nums[i] > leftMax) {
+                    leftMax = nums[i];
+                    valid[i] = true;
+                }
+            }
+            int rightMax = nums[nums.length - 1];
+            for (int i = nums.length - 2; i >= 0; i--) {
+                if (nums[i] > rightMax) {
+                    rightMax = nums[i];
+                    valid[i] = true;
+                }
+            }
+            List<Integer> result = new ArrayList<>();
+            for (int i = 0; i < nums.length; i++) {
+                if (valid[i]) {
+                    result.add(nums[i]);
+                }
+            }
+            return result;
+        }
+    }
+}

src/test/java/com/fishercoder/fourththousand/_3912Test.java

@@ -0,0 +1,24 @@
+package com.fishercoder.fourththousand;
+
+import com.fishercoder.solutions.fourththousand._3912;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class _3912Test {
+    private _3912.Solution1 solution1;
+
+    @BeforeEach
+    public void setup() {
+        solution1 = new _3912.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(new ArrayList<>(Arrays.asList(1, 2, 4, 3, 2)), solution1.findValidElements(new int[]{1, 2, 4, 2, 3, 2}));
+    }
+}