add: randomized quick sort solution for Miscellaneous

Miscellaneous/randomize-quick-sort.go

@@ -0,0 +1,49 @@
+package Miscellaneous
+
+import (
+	"math/rand"
+	"time"
+)
+
+//
+// coverage time complexity: O(n), worst O(n^2)
+// space complexity: O(n)
+//
+func findKthSmallestNumberUsingRandomQuickSort(nums []int, k int) int {
+	if k > len(nums) {
+		return -1
+	}
+	return recursiveFindPivot(nums, k, 0, len(nums)-1)
+}
+
+func recursiveFindPivot(nums []int, k, start, end int) int {
+	p := partitionRandomized(nums, start, end)
+	if p == k-1 {
+		return nums[p]
+	}
+	if p > k-1 {
+		return recursiveFindPivot(nums, k, start, p-1)
+	}
+	return recursiveFindPivot(nums, k, p+1, end)
+}
+
+func partitionRandomized(nums []int, low, high int) int {
+	if low == high {
+		return low
+	}
+
+	rand.Seed(time.Now().Unix())
+	pivot_ind := low + rand.Intn(high-low)
+	nums[pivot_ind], nums[high] = nums[high], nums[pivot_ind]
+
+	pivot := nums[high]
+	i := low - 1
+	for j := low; j < high; j++ {
+		if nums[j] < pivot {
+			i++
+			nums[i], nums[j] = nums[j], nums[i]
+		}
+	}
+	nums[i+1], nums[high] = nums[high], nums[i+1]
+	return i + 1
+}

Miscellaneous/randomize-quick-sort_test.go

@@ -0,0 +1,27 @@
+package Miscellaneous
+
+import "testing"
+
+func Test_findKthSmallestNumberUsingRandomQuickSort(t *testing.T) {
+	type args struct {
+		nums []int
+		k    int
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{"case1", args{[]int{1, 5, 12, 2, 11, 5}, 3}, 5},
+		{"case2", args{[]int{1, 5, 12, 2, 11, 5}, 4}, 5},
+		{"case3", args{[]int{5, 12, 11, -1, 12}, 3}, 11},
+		{"case4", args{[]int{5, 12, 11, -1, 12}, 6}, -1},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := findKthSmallestNumberUsingRandomQuickSort(tt.args.nums, tt.args.k); got != tt.want {
+				t.Errorf("findKthSmallestNumberUsingRandomQuickSort() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}