Add problem 215 - Kth Largest Element In An Array

Author: anirudhology

problems/quick_select/kth_largest_element_in_an_array.go

@@ -0,0 +1,30 @@
+package quick_select
+
+func FindKthLargestElementInAnArray(nums []int, k int) int {
+	k = len(nums) - k
+	left, right := 0, len(nums)-1
+	for left < right {
+		pivotIndex := partition(nums, left, right)
+		if pivotIndex < k {
+			left = pivotIndex + 1
+		} else if pivotIndex > k {
+			right = pivotIndex - 1
+		} else {
+			break
+		}
+	}
+	return nums[k]
+}
+
+func partition(nums []int, left, right int) int {
+	pivot := nums[right]
+	pivotIndex := left
+	for i := left; i < right; i++ {
+		if nums[i] <= pivot {
+			nums[pivotIndex], nums[i] = nums[i], nums[pivotIndex]
+			pivotIndex++
+		}
+	}
+	nums[right], nums[pivotIndex] = nums[pivotIndex], nums[right]
+	return pivotIndex
+}

tests/quick_select/kth_largest_element_in_an_array_test.go

@@ -0,0 +1,25 @@
+package quick_select_test
+
+import (
+	"testing"
+
+	"github.com/anirudhology/leetcode-go/problems/quick_select"
+)
+
+func TestFindKthLargest(t *testing.T) {
+	if res := quick_select.FindKthLargestElementInAnArray([]int{3, 2, 1, 5, 6, 4}, 2); res != 5 {
+		t.Errorf("expected 5, got %v", res)
+	}
+	if res := quick_select.FindKthLargestElementInAnArray([]int{3, 2, 3, 1, 2, 4, 5, 5, 6}, 4); res != 4 {
+		t.Errorf("expected 4, got %v", res)
+	}
+	if res := quick_select.FindKthLargestElementInAnArray([]int{1}, 1); res != 1 {
+		t.Errorf("expected 1, got %v", res)
+	}
+	if res := quick_select.FindKthLargestElementInAnArray([]int{1, 2}, 1); res != 2 {
+		t.Errorf("expected 2, got %v", res)
+	}
+	if res := quick_select.FindKthLargestElementInAnArray([]int{-1, -1}, 2); res != -1 {
+		t.Errorf("expected -1, got %v", res)
+	}
+}