add 961

Author: fishercoder1534

README.md

@@ -29,6 +29,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|---------------|---------------|--------|-------------|-------------
+|961|[N-Repeated Element in Size 2N Array](https://leetcode.com/problems/n-repeated-element-in-size-2n-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_961.java) | O(n) | O(1) | |Easy|
 |944|[Delete Columns to Make Sorted](https://leetcode.com/problems/delete-columns-to-make-sorted/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_944.java) | O(n) | O(1) | |Easy|
 |941|[Valid Mountain Array](https://leetcode.com/problems/valid-mountain-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_941.java) | O(n) | O(1) | |Easy|
 |933|[Number of Recent Calls](https://leetcode.com/problems/number-of-recent-calls/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_933.java) | O(n) | O(n) | |Easy|

src/main/java/com/fishercoder/solutions/_961.java

@@ -0,0 +1,45 @@
+package com.fishercoder.solutions;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * 961. N-Repeated Element in Size 2N Array
+ *
+ * In a array A of size 2N, there are N+1 unique elements, and exactly one of these elements is repeated N times.
+ *
+ * Return the element repeated N times.
+ *
+ * Example 1:
+ *
+ * Input: [1,2,3,3]
+ * Output: 3
+ * Example 2:
+ *
+ * Input: [2,1,2,5,3,2]
+ * Output: 2
+ * Example 3:
+ *
+ * Input: [5,1,5,2,5,3,5,4]
+ * Output: 5
+ *
+ *
+ * Note:
+ *
+ * 4 <= A.length <= 10000
+ * 0 <= A[i] < 10000
+ * A.length is even
+ * */
+public class _961 {
+    public static class Solution1 {
+        public int repeatedNTimes(int[] A) {
+            Set<Integer> set = new HashSet<>();
+            for (int num : A) {
+                if (!set.add(num)) {
+                    return num;
+                }
+            }
+            return -1;
+        }
+    }
+}

src/test/java/com/fishercoder/_961Test.java

@@ -0,0 +1,36 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._961;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class _961Test {
+    private static _961.Solution1 solution1;
+    private static int[] A;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _961.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        A = new int[]{1, 2, 3, 3};
+        assertEquals(3, solution1.repeatedNTimes(A));
+    }
+
+    @Test
+    public void test2() {
+        A = new int[]{2, 1, 2, 5, 3, 2};
+        assertEquals(2, solution1.repeatedNTimes(A));
+    }
+
+    @Test
+    public void test3() {
+        A = new int[]{5, 1, 5, 2, 5, 3, 5, 4};
+        assertEquals(5, solution1.repeatedNTimes(A));
+    }
+
+}