add Java solution for 2001

fishercoder1534 · fishercoder1534 · commit 078a2ca7f81c · 2021-09-12T09:24:13.000-07:00
diff --git a/README.md b/README.md
@@ -8,7 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                  
 |-----|----------------|---------------|--------|-------------|-------------
-|2001|[Number of Pairs of Interchangeable Rectangles](https://leetcode.com/problems/number-of-pairs-of-interchangeable-rectangles/)|[Python3](../master/python3/2001.py) ||Medium||
+|2001|[Number of Pairs of Interchangeable Rectangles](https://leetcode.com/problems/number-of-pairs-of-interchangeable-rectangles/)|[Python3](../master/python3/2001.py), [Java](../master/src/main/java/com/fishercoder/solutions/_2001.java) ||Medium||
 |2000|[Reverse Prefix of Word](https://leetcode.com/problems/reverse-prefix-of-word/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_2000.java) ||Easy||
 |1996|[The Number of Weak Characters in the Game](https://leetcode.com/problems/the-number-of-weak-characters-in-the-game/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1996.java) ||Medium||
 |1995|[Count Special Quadruplets](https://leetcode.com/problems/count-special-quadruplets/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1995.java) ||Easy||
diff --git a/src/main/java/com/fishercoder/solutions/_2001.java b/src/main/java/com/fishercoder/solutions/_2001.java
@@ -0,0 +1,25 @@
+package com.fishercoder.solutions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class _2001 {
+    public static class Solution1 {
+        /**
+         * credit: https://github.com/fishercoder1534/Leetcode/blob/master/python3/2001.py
+         */
+        public long interchangeableRectangles(int[][] rectangles) {
+            Map<Double, Integer> map = new HashMap<>();
+            for (int[] rec : rectangles) {
+                double ratio = (double) rec[0] / rec[1];
+                map.put(ratio, map.getOrDefault(ratio, 0) + 1);
+            }
+            long answer = 0;
+            for (double ratio : map.keySet()) {
+                int count = map.get(ratio);
+                answer += (long) count * (count - 1) / 2;
+            }
+            return answer;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_2001Test.java b/src/test/java/com/fishercoder/_2001Test.java
@@ -0,0 +1,22 @@
+package com.fishercoder;
+
+import com.fishercoder.common.utils.CommonUtils;
+import com.fishercoder.solutions._2001;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _2001Test {
+    private static _2001.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _2001.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(6, solution1.interchangeableRectangles(CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[4,8],[3,6],[10,20],[15,30]")));
+    }
+}
