add 1331

Author: fishercoder1534

README.md

@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ ★
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1331|[Rank Transform of an Array](https://leetcode.com/problems/rank-transform-of-an-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1331.java) | |Easy||
 |1317|[Convert Integer to the Sum of Two No-Zero Integers](https://leetcode.com/problems/convert-integer-to-the-sum-of-two-no-zero-integers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1317.java) | |Easy||
 |1305|[All Elements in Two Binary Search Trees](https://leetcode.com/problems/all-elements-in-two-binary-search-trees/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1305.java) | |Medium||
 |1304|[Find N Unique Integers Sum up to Zero](https://leetcode.com/problems/find-n-unique-integers-sum-up-to-zero/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1304.java) | |Easy||

src/main/java/com/fishercoder/solutions/_1331.java

@@ -0,0 +1,53 @@
+package com.fishercoder.solutions;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeSet;
+
+/**
+ * 1331. Rank Transform of an Array
+ *
+ * Given an array of integers arr, replace each element with its rank.
+ * The rank represents how large the element is. The rank has the following rules:
+ * Rank is an integer starting from 1.
+ * The larger the element, the larger the rank. If two elements are equal, their rank must be the same.
+ * Rank should be as small as possible.
+ *
+ * Example 1:
+ * Input: arr = [40,10,20,30]
+ * Output: [4,1,2,3]
+ * Explanation: 40 is the largest element. 10 is the smallest. 20 is the second smallest. 30 is the third smallest.
+ *
+ * Example 2:
+ * Input: arr = [100,100,100]
+ * Output: [1,1,1]
+ * Explanation: Same elements share the same rank.
+ *
+ * Example 3:
+ * Input: arr = [37,12,28,9,100,56,80,5,12]
+ * Output: [5,3,4,2,8,6,7,1,3]
+ *
+ * Constraints:
+ * 0 <= arr.length <= 105
+ * -109 <= arr[i] <= 109
+ * */
+public class _1331 {
+    public static class Solution1 {
+        public int[] arrayRankTransform(int[] arr) {
+            TreeSet<Integer> set = new TreeSet<>();
+            for (int i : arr) {
+                set.add(i);
+            }
+            Map<Integer, Integer> map = new HashMap<>();
+            int rank = 1;
+            for (int num : set) {
+                map.put(num, rank++);
+            }
+            int[] ranks = new int[arr.length];
+            for (int i = 0; i < arr.length; i++) {
+                ranks[i] = map.get(arr[i]);
+            }
+            return ranks;
+        }
+    }
+}

src/test/java/com/fishercoder/_1331Test.java

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+package com.fishercoder;
+
+import com.fishercoder.solutions._1331;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class _1331Test {
+    private static _1331.Solution1 solution1;
+    private static int[] arr;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1331.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        arr = new int[]{40, 10, 20, 30};
+        assertArrayEquals(new int[]{4, 1, 2, 3}, solution1.arrayRankTransform(arr));
+    }
+
+    @Test
+    public void test2() {
+        arr = new int[]{100, 100, 100};
+        assertArrayEquals(new int[]{1, 1, 1}, solution1.arrayRankTransform(arr));
+    }
+
+    @Test
+    public void test3() {
+        arr = new int[]{-1, -3, 100};
+        assertArrayEquals(new int[]{2, 1, 3}, solution1.arrayRankTransform(arr));
+    }
+}