add 1399

Author: fishercoder1534

README.md

@@ -9,6 +9,7 @@ _If you like this project, please leave me a star._ ★
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
 |1400|[Construct K Palindrome Strings](https://leetcode.com/problems/construct-k-palindrome-strings/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1400.java) | |Medium|Greedy|
+|1399|[Count Largest Group](https://leetcode.com/problems/count-largest-group/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1399.java) | |Easy|Array|
 |1396|[Design Underground System](https://leetcode.com/problems/design-underground-system/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1396.java) | |Medium|Design|
 |1395|[Count Number of Teams](https://leetcode.com/problems/count-number-of-teams/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1395.java) | |Medium|Array|
 |1394|[Find Lucky Integer in an Array](https://leetcode.com/problems/find-lucky-integer-in-an-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1394.java) | |Easy|Array|

src/main/java/com/fishercoder/solutions/_1399.java

@@ -0,0 +1,69 @@
+package com.fishercoder.solutions;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * 1399. Count Largest Group
+ *
+ * Given an integer n. Each number from 1 to n is grouped according to the sum of its digits.
+ * Return how many groups have the largest size.
+ *
+ * Example 1:
+ * Input: n = 13
+ * Output: 4
+ * Explanation: There are 9 groups in total, they are grouped according sum of its digits of numbers from 1 to 13:
+ * [1,10], [2,11], [3,12], [4,13], [5], [6], [7], [8], [9]. There are 4 groups with largest size.
+ *
+ * Example 2:
+ * Input: n = 2
+ * Output: 2
+ * Explanation: There are 2 groups [1], [2] of size 1.
+ *
+ * Example 3:
+ * Input: n = 15
+ * Output: 6
+ *
+ * Example 4:
+ * Input: n = 24
+ * Output: 5
+ *
+ * Constraints:
+ * 1 <= n <= 10^4
+ * */
+public class _1399 {
+    public static class Solution1 {
+        public int countLargestGroup(int n) {
+            Map<Integer, List<Integer>> map = new HashMap<>();
+            for (int i = 1; i <= n; i++) {
+                int sumOfDigits = getSum(i);
+                if (!map.containsKey(sumOfDigits)) {
+                    map.put(sumOfDigits, new ArrayList<>());
+                }
+                map.get(sumOfDigits).add(i);
+            }
+            int max = 0;
+            for (int key : map.keySet()) {
+                max = Math.max(max, map.get(key).size());
+            }
+            int count = 0;
+            for (int key : map.keySet()) {
+                if (map.get(key).size() == max) {
+                    count++;
+                }
+            }
+            return count;
+        }
+
+        private int getSum(int num) {
+            int sum = 0;
+            while (num != 0) {
+                sum += num % 10;
+                num /= 10;
+            }
+            return sum;
+        }
+    }
+}

src/test/java/com/fishercoder/_1399Test.java

@@ -0,0 +1,37 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1399;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1399Test {
+    private static _1399.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1399.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(4, solution1.countLargestGroup(13));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(2, solution1.countLargestGroup(2));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(6, solution1.countLargestGroup(15));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(5, solution1.countLargestGroup(24));
+    }
+
+}