Add Geometric Sequence Triplets

Author: marttp

kotlin/Hash Maps and Sets/GeometricSequenceTriplets.kt

@@ -0,0 +1,25 @@
+fun geometricSequenceTriplets(nums: List<Int>, r: Int): Int {
+    // leftMap and rightMap will use 'getOrDefault' to ensure the default value of 0 is returned when
+    // accessing a key that doesn’t exist in the hash map. This effectively sets
+    // the default frequency of all elements to 0.
+    val leftMap = mutableMapOf<Int, Int>()
+    val rightMap = mutableMapOf<Int, Int>()
+    var count = 0
+    // Populate 'rightMap' with the frequency of each element in the array.
+    for (x in nums) {
+        rightMap[x] = rightMap.getOrDefault(x, 0) + 1
+    }
+    // Search for geometric triplets that have x as the center.
+    for (x in nums) {
+        // Decrement the frequency of x in 'rightMap' since x is now being
+        // processed and is no longer to the right.
+        rightMap[x] = rightMap.getOrDefault(x, 0) - 1
+        if (x % r == 0) {
+            count += leftMap.getOrDefault(x / r, 0) * rightMap.getOrDefault(x * r, 0)
+        }
+        // Increment the frequency of x in 'leftMap' since it'll be a part of the
+        // left side of the array once we iterate to the next value of x.
+        leftMap[x] = leftMap.getOrDefault(x, 0) + 1
+    }
+    return count
+}