算法实现系列第三章.快速排序

先剽窃jdk的...

package algorithm;

import java.util.Arrays;

/**
 * 快速排序,哦也
 * 
 * @author ansj
 * 
 */
public class QuickSort {
	public static void main(String[] args) {
		long[] ints = { 123, 1234, 324, 2, 1, 12, 31, 4, 3, 3, 466, 7, 87, 87, 56, 456, 5 };
		sort(ints, 0, ints.length);
		for (int i = 0; i < ints.length; i++) {
			System.out.println(ints[i]);
		}
	}

	private static void sort(long x[], int off, int len) {
		// Insertion sort on smallest arrays
		if (len < 7) {
			for (int i = off; i < len + off; i++)
				for (int j = i; j > off && x[j - 1] > x[j]; j--)
					swap(x, j, j - 1);
			return;
		}

		// Choose a partition element, v
		int m = off + (len >> 1); // Small arrays, middle element
		if (len > 7) {
			int l = off;
			int n = off + len - 1;
			if (len > 40) { // Big arrays, pseudomedian of 9
				int s = len / 8;
				l = med3(x, l, l + s, l + 2 * s);
				m = med3(x, m - s, m, m + s);
				n = med3(x, n - 2 * s, n - s, n);
			}
			m = med3(x, l, m, n); // Mid-size, med of 3
		}
		long v = x[m];

		// Establish Invariant: v* (<v)* (>v)* v*
		int a = off, b = a, c = off + len - 1, d = c;
		while (true) {
			while (b <= c && x[b] <= v) {
				if (x[b] == v)
					swap(x, a++, b);
				b++;
			}
			while (c >= b && x[c] >= v) {
				if (x[c] == v)
					swap(x, c, d--);
				c--;
			}
			if (b > c)
				break;
			swap(x, b++, c--);
		}

		// Swap partition elements back to middle
		int s, n = off + len;
		s = Math.min(a - off, b - a);
		vecswap(x, off, b - s, s);
		s = Math.min(d - c, n - d - 1);
		vecswap(x, b, n - s, s);

		// Recursively sort non-partition-elements
		if ((s = b - a) > 1)
			sort(x, off, s);
		if ((s = d - c) > 1)
			sort(x, n - s, s);
	}

	private static int med3(long x[], int a, int b, int c) {
		return (x[a] < x[b] ? (x[b] < x[c] ? b : x[a] < x[c] ? c : a) : (x[b] > x[c] ? b : x[a] > x[c] ? c : a));
	}

	/**
	 * Swaps x[a .. (a+n-1)] with x[b .. (b+n-1)].
	 */
	private static void vecswap(long x[], int a, int b, int n) {
		for (int i = 0; i < n; i++, a++, b++)
			swap(x, a, b);
	}

	/**
	 * Swaps x[a] with x[b].
	 */
	private static void swap(long x[], int a, int b) {
		long t = x[a];
		x[a] = x[b];
		x[b] = t;
	}
}