Merge pull request neetcode-gh#1445 from t3chkid/main

Adds solution that uses "Quick Select" algorithm for "215. Kth Largest element in an Array" in Kotlin

Author: Ahmad-A0

kotlin/215-Kth-Largest-Element-In-Array.kt

@@ -11,4 +11,42 @@ class Solution {
 
         return heap.peek()
     }
+
+    // O(n) average time complexity - Quick Select algorithm
+    fun findKthLargestRecursive(nums: IntArray, k: Int): Int = quickSelect(
+        array = nums,
+        startIndex = 0,
+        endIndex = nums.lastIndex,
+        k = k
+    )
+
+    private fun quickSelect(
+        array: IntArray,
+        startIndex: Int,
+        endIndex: Int,
+        k: Int,
+    ): Int {
+        // find a valid position for pivot such that all values that
+        // appear before the pivot are lower than the value of pivot,
+        // and, all values that appear after the pivot are greater
+        // than the pivot.
+        @Suppress("UnnecessaryVariable") val pivotIndex = endIndex
+        var validIndexForPivot = startIndex
+        for (i in startIndex until endIndex) {
+            if (array[i] < array[pivotIndex]) {
+                val temp = array[i]
+                array[i] = array[validIndexForPivot]
+                array[validIndexForPivot] = temp
+                validIndexForPivot++
+            }
+        }
+        // put pivot element in it's sorted position
+        val temp = array[validIndexForPivot]
+        array[validIndexForPivot] = array[pivotIndex]
+        array[pivotIndex] = temp
+
+        return if (validIndexForPivot == (array.size - k)) array[validIndexForPivot]
+        else if (validIndexForPivot > array.size - k) quickSelect(array, startIndex, validIndexForPivot - 1, k)
+        else quickSelect(array, validIndexForPivot + 1, endIndex, k)
+    }
 }