| # | 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||

packagecom.fishercoder.solutions;

importjava.util.HashMap;

importjava.util.Map;

publicclass_2001 {

publicstaticclassSolution1 {

publiclonginterchangeableRectangles(int[][]rectangles) {

Map<Double,Integer>map =newHashMap<>();

for (int[]rec :rectangles) {

doubleratio = (double)rec[0] /rec[1];

map.put(ratio,map.getOrDefault(ratio,0) +1);

}

longanswer =0;

for (doubleratio :map.keySet()) {

intcount =map.get(ratio);

answer += (long)count * (count -1) /2;

}

returnanswer;

}

}

}

packagecom.fishercoder;

importcom.fishercoder.common.utils.CommonUtils;

importcom.fishercoder.solutions._2001;

importorg.junit.BeforeClass;

importorg.junit.Test;

importstaticorg.junit.Assert.assertEquals;

publicclass_2001Test {

privatestatic_2001.Solution1solution1;

publicstaticvoidsetup() {

solution1 =new_2001.Solution1();

}

publicvoidtest1() {

assertEquals(6,solution1.interchangeableRectangles(CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[4,8],[3,6],[10,20],[15,30]")));

}

}