add 1429

Author: fishercoder1534

README.md

@@ -298,6 +298,7 @@ _If you like this project, please leave me a star._ ★
 |1436|[Destination City](https://leetcode.com/problems/destination-city/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1436.java) | |Easy|String|
 |1432|[Max Difference You Can Get From Changing an Integer](https://leetcode.com/problems/max-difference-you-can-get-from-changing-an-integer/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1432.java) | |Medium|String|
 |1431|[Kids With the Greatest Number of Candies](https://leetcode.com/problems/kids-with-the-greatest-number-of-candies/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1431.java), [C++](../master/cpp/_1431.cpp) | |Easy|Array|
+|1429|[First Unique Number](https://leetcode.com/problems/first-unique-number/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1429.java) | |Medium|Array, HashTable, Design, Data Streams|
 |1428|[Leftmost Column with at Least a One](https://leetcode.com/problems/leftmost-column-with-at-least-a-one/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1428.java) | |Medium|Array|
 |1427|[Perform String Shifts](https://leetcode.com/problems/perform-string-shifts/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1427.java) | |Easy|Array, Math|
 |1426|[Counting Elements](https://leetcode.com/problems/counting-elements/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1426.java) | |Easy|Array|

src/main/java/com/fishercoder/solutions/_1429.java

@@ -0,0 +1,45 @@
+package com.fishercoder.solutions;
+
+import java.util.HashSet;
+import java.util.LinkedHashSet;
+import java.util.Set;
+
+public class _1429 {
+    public static class Solution1 {
+        /**
+         * Credit: https://leetcode.com/problems/first-unique-number/discuss/602698/Java-Easy-Set-O(1)
+         * <p>
+         * LinkedHashSet is a handy data structure to help preserve the order of all unique elements.
+         */
+        public static class FirstUnique {
+
+            Set<Integer> uniqSet;
+            Set<Integer> nonUniqSet;
+
+            public FirstUnique(int[] nums) {
+                uniqSet = new LinkedHashSet<>();
+                nonUniqSet = new HashSet<>();
+                for (int num : nums) {
+                    add(num);
+                }
+            }
+
+            public int showFirstUnique() {
+                if (!uniqSet.isEmpty()) {
+                    return uniqSet.iterator().next();
+                }
+                return -1;
+            }
+
+            public void add(int value) {
+                if (uniqSet.contains(value)) {
+                    uniqSet.remove(value);
+                    nonUniqSet.add(value);
+                }
+                if (!nonUniqSet.contains(value)) {
+                    uniqSet.add(value);
+                }
+            }
+        }
+    }
+}