Untitled

import java.util.Random;

public class QuickSelect {
    public int findKthSmallest(int[] nums, int k) {
        // Convert k-th smallest to 0-based index
        int targetIndex = k - 1;

        int left = 0, right = nums.length - 1;
        Random rand = new Random();

        while (left <= right) {
            // Select a random pivot index
            int pivotIndex = left + rand.nextInt(right - left + 1);

            // Partition the array and get the pivot's final position
            int finalPivotIndex = partition(nums, left, right, pivotIndex);

            if (finalPivotIndex == targetIndex) {
                return nums[finalPivotIndex]; // Found the k-th smallest element
            } else if (finalPivotIndex < targetIndex) {
                left = finalPivotIndex + 1; // Search right subarray
            } else {
                right = finalPivotIndex - 1; // Search left subarray
            }
        }

        return -1; // This should never be reached if k is valid
    }

    private int partition(int[] nums, int left, int right, int pivotIndex) {
        int pivotValue = nums[pivotIndex];
        // Move pivot to the end
        swap(nums, pivotIndex, right);
        int storeIndex = left;

        // Move all elements smaller than pivot to the left
        for (int i = left; i < right; i++) {
            if (nums[i] < pivotValue) {
                swap(nums, i, storeIndex);
                storeIndex++;
            }
        }

        // Move pivot to its final position
        swap(nums, storeIndex, right);
        return storeIndex;
    }

    private void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }

    public static void main(String[] args) {
        QuickSelect qs = new QuickSelect();
        int[] nums = {3, 2, 1, 5, 6, 4};
        int k = 2; // Find the 2nd smallest element
        System.out.println("K-th smallest element: " + qs.findKthSmallest(nums, k)); // Output: 2
    }
}