/*
 * 利用快排尋找陣列中第k個最大元素
 */
public class FindFirstKElement {
	//快排
	public static int getBaseIndex(int[] arr, int start, int end) {
		int base = arr[start];
		while(start < end) {
			while(arr[end] > base && end > start) {
				end --;
			}
			if(end <= start) {
				break;
			}
			else {
				int temp = arr[end];
				arr[end] = arr[start];
				arr[start] = temp;
			}
			while(arr[start] < base && start < end) {
				start ++;
			}
			if(start >= end) {
				break;
			}
			else {
				int temp = arr[start];
				arr[start] = arr[end];
				arr[end] = temp;
			}
		}
		return start;
	}
	
	public static void findFirstKElement(int[] arr, int k, int start, int end) {
		int middle = getBaseIndex(arr, start, end);
		if(middle == k - 1) {
			System.out.println(arr[middle]);
		}
		else if(middle < k - 1) {  //middle右邊找
			findFirstKElement(arr, k, middle + 1, end);
		}
		else {	//middle左邊找
			findFirstKElement(arr, k, start, middle - 1);
		}
	}
	
	public static void main(String[] args) {
		int[] arr = {23,4,6,8,232};
		int k = 2;
		int start = 0;
		int end = arr.length - 1;
		findFirstKElement(arr, k, start, end);
	}
}