add 781

Author: fishercoder1534

README.md

@@ -362,6 +362,7 @@ _If you like this project, please leave me a star._ ★
 |788|[Rotated Digits](https://leetcode.com/problems/rotated-digits/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_788.java) | |Easy|
 |784|[Letter Case Permutation](https://leetcode.com/problems/letter-case-permutation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_784.java) |  |Easy|
 |783|[Minimum Distance Between BST Nodes](https://leetcode.com/problems/minimum-distance-between-bst-nodes/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_783.java) |  |Easy|
+|781|[Rabbits in Forest](https://leetcode.com/problems/rabbits-in-forest/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_781.java) |  |Medium| HashTable, Math
 |779|[K-th Symbol in Grammar](https://leetcode.com/problems/k-th-symbol-in-grammar/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_779.java) |  |Medium|
 |776|[Split BST](https://leetcode.com/problems/split-bst/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_776.java) | |Medium| Recursion
 |771|[Jewels and Stones](https://leetcode.com/problems/jewels-and-stones/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_771.java) |  |Easy|

src/main/java/com/fishercoder/solutions/_781.java

@@ -0,0 +1,31 @@
+package com.fishercoder.solutions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class _781 {
+    public static class Solution1 {
+        public int numRabbits(int[] answers) {
+            Map<Integer, Integer> map = new HashMap<>();
+            int rabbits = 0;
+            for (int rabbitType : answers) {
+                if (map.containsKey(rabbitType)) {
+                    int count = map.get(rabbitType);
+                    count--;
+                    if (count == 0) {
+                        map.remove(rabbitType);
+                    } else {
+                        map.put(rabbitType, count);
+                    }
+                } else {
+                    rabbits += rabbitType;
+                    rabbits++;
+                    if (rabbitType != 0) {
+                        map.put(rabbitType, rabbitType);
+                    }
+                }
+            }
+            return rabbits;
+        }
+    }
+}

src/test/java/com/fishercoder/_781Test.java

@@ -0,0 +1,46 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._781;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _781Test {
+    private static _781.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _781.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(5, solution1.numRabbits(new int[]{1, 1, 2}));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(11, solution1.numRabbits(new int[]{10, 10, 10}));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(0, solution1.numRabbits(new int[]{}));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(5, solution1.numRabbits(new int[]{1, 0, 1, 0, 0}));
+    }
+
+    @Test
+    public void test5() {
+        assertEquals(7, solution1.numRabbits(new int[]{1, 1, 1, 2, 2, 2}));
+    }
+
+    @Test
+    public void test6() {
+        assertEquals(13, solution1.numRabbits(new int[]{2, 1, 2, 2, 2, 2, 2, 2, 1, 1}));
+    }
+}