Added solution to count triplets hackerrank problem

Author: kanahaiya

HackerRankDashboard/Interview-Preparation-Kit/src/main/java/com/javaaid/dictionaries/CountTriplets.java

@@ -0,0 +1,64 @@
+/**
+ * 
+ * Problem Statement-
+ * [Count Triplets](https://www.hackerrank.com/challenges/count-triplets-1/problem) 
+ * [Tutorial]()
+ * 
+ */
+package com.javaaid.dictionaries;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Scanner;
+
+public class CountTriplets {
+
+	private static long countTriplets(List<Long> arr, long r) {
+		Map<Long, Long> leftMap = new HashMap<>();
+		Map<Long, Long> rightMap = new HashMap<>();
+
+		for (long item : arr) {
+			rightMap.put(item, rightMap.getOrDefault(item, 0L) + 1);
+		}
+
+		long count = 0;
+
+		for (int i = 0; i < arr.size(); i++) {
+			long midTerm = arr.get(i);
+			long c1 = 0, c3 = 0;
+
+			rightMap.put(midTerm, rightMap.getOrDefault(midTerm, 0L) - 1);
+
+			if (leftMap.containsKey(midTerm / r) && midTerm % r == 0) {
+				c1 = leftMap.get(midTerm / r);
+			}
+
+			if (rightMap.containsKey(midTerm * r))
+				c3 = rightMap.get(midTerm * r);
+
+			count += c1 * c3;
+
+			leftMap.put(midTerm, leftMap.getOrDefault(midTerm, 0L) + 1);
+
+		}
+		return count;
+	}
+
+	public static void main(String[] args) throws IOException {
+		Scanner sc = new Scanner(System.in);
+		long n = sc.nextLong();
+		long r = sc.nextLong();
+		List<Long> arr = new ArrayList<>();
+		while (n-- > 0) {
+			arr.add(sc.nextLong());
+		}
+
+		long ans = countTriplets(arr, r);
+		System.out.println(ans);
+
+		sc.close();
+	}
+}