java 的一些排序方法

一些java排序方法,记录下。

package com.taobao.junyu.fastnet.util;

import java.util.Arrays;
import java.util.List;

public class SortUtil {
	private static int CUTOFF = 10;

	/**
	 * Simple insertion sort
	 * 
	 * @param a
	 *            an array of Comparable items
	 */
	public static <T extends Comparable<? super T>> void insertionSort(T[] a) {
		insertionSort(a, 0, a.length - 1);
	}

	/**
	 * Simple bubble sort
	 * 
	 * @param a
	 *            an array of Comparable items
	 */
	public static <T extends Comparable<? super T>> void bubbleSort(T[] a) {
		for (int i = 0; i < a.length - 1; i++) // the last one is no need for
												// comparing to itself
		{
			for (int j = a.length - 1; j > i; j--) {
				if (a[j].compareTo(a[j - 1]) < 0) {
					swapReferences(a, j, j - 1);
				}
			}
		}
	}

	/**
	 * Shell sort, using Shell's (poor) increments.
	 * 
	 * @param a
	 *            an array of Comparable items
	 */
	public static <T extends Comparable<? super T>> void shellSort(T[] a) {
		int j;
		for (int gap = a.length / 2; gap > 0; gap /= 2) {
			for (int i = gap; i < a.length; i++) {
				T tmp = a[i];
				for (j = i; j >= gap && tmp.compareTo(a[j - gap]) < 0; j -= gap) {
					a[j] = a[j - gap];
				}
				a[j] = tmp;
			}
		}
	}

	/**
	 * Simple selection sort
	 * 
	 * @param a
	 *            an array of Comparable items
	 */
	public static <T extends Comparable<? super T>> void selectionSort(T[] a) {
		for (int i = 0; i < a.length - 1; i++) {
			int minIdx = i;
			for (int j = i + 1; j < a.length; j++) {
				if (a[j].compareTo(a[minIdx]) < 0)
					minIdx = j;
			}
			if (minIdx != i) {
				swapReferences(a, i, minIdx);
			}
		}
	}

	/**
	 * Standard heap sort
	 * 
	 * @param a
	 *            an array of Comparable items
	 */
	public static <T extends Comparable<? super T>> void heapSort(T[] a) {
		for (int i = a.length / 2; i >= 0; i--) /* buildHeap */
		{
			percDown(a, i, a.length);
		}

		for (int i = a.length - 1; i > 0; i--) {
			swapReferences(a, 0, i); /* deleteMax */
			percDown(a, 0, i);
		}
	}

	/**
	 * Merge sort algorithm
	 * 
	 * @param a
	 *            an array of Comparable items
	 */
	public static <T extends Comparable<? super T>> void mergeSort(T[] a) {
		@SuppressWarnings("unchecked")
		T[] tmpArray = (T[]) new Comparable[a.length];
		mergeSort(a, tmpArray, 0, a.length - 1);
	}

	/**
	 * Quick sort algorithm
	 * 
	 * @param a
	 *            an array of Comparable items
	 */
	public static <T extends Comparable<? super T>> void quickSort(T[] a) {
		quickSort(a, 0, a.length - 1);
	}

	/**
	 * Internal method for heap sort that is used in deleteMax an buildHeap
	 * 
	 * @param a
	 *            an array of Comparable items.
	 * @param i
	 *            the position from which to percolate down.
	 * @param n
	 *            the logical size of binary heap.
	 */
	private static <T extends Comparable<? super T>> void percDown(T[] a,
			int i, int n) {
		int child;
		T tmp;

		for (tmp = a[i]; leftChild(i) < n; i = child) {
			child = leftChild(i);
			if (child != n - 1 && a[child].compareTo(a[child + 1]) < 0)
				child++;
			if (tmp.compareTo(a[child]) < 0)

				a[i] = a[child];
			else
				break;
		}
		a[i] = tmp;
	}

	/**
	 * Internal method for heap sort.
	 * 
	 * @param i
	 *            the index of an item in the heap
	 * @return the index of the left heap
	 */
	private static int leftChild(int i) {
		return 2 * i + 1;
	}

	/**
	 * Internal method that makes recursive calls.
	 * 
	 * @param a
	 *            an array of Comparable items.
	 * @param tmpArray
	 *            an array to place the merged result.
	 * @param left
	 *            the left-most index of the sub-array.
	 * @param right
	 *            the right-most index of the sub-array.
	 */
	private static <T extends Comparable<? super T>> void mergeSort(T[] a,
			T[] tmpArray, int left, int right) {
		if (left < right) {
			int center = (left + right) / 2;
			mergeSort(a, tmpArray, left, center);
			mergeSort(a, tmpArray, center + 1, right);
			merge(a, tmpArray, left, center + 1, right);
		}
	}

	/**
	 * Internal method that merges two sorted halves of a sub-array
	 * 
	 * @param a
	 *            an array of Comparable items
	 * @param tmpArray
	 *            an array to place the merged result.
	 * @param leftPos
	 *            the left-most index of the sub-array.
	 * @param rightPos
	 *            the index of the start of the second half.
	 * @param rightEnd
	 *            the right-most index of the sub-array.
	 */
	private static <T extends Comparable<? super T>> void merge(T[] a,
			T[] tmpArray, int leftPos, int rightPos, int rightEnd) {
		int leftEnd = rightPos - 1;
		int tmpPos = leftPos;
		int numElements = rightEnd - leftPos + 1;

		// Main loop
		while (leftPos <= leftEnd && rightPos <= rightEnd) {
			if (a[leftPos].compareTo(a[rightPos]) <= 0) {
				tmpArray[tmpPos++] = a[leftPos++];
			} else {
				tmpArray[tmpPos++] = a[rightPos++];
			}
		}

		while (leftPos <= leftEnd)
			// Copy rest of first half
			tmpArray[tmpPos++] = a[leftPos++];

		while (rightPos <= rightEnd)
			// Copy rest of second half
			tmpArray[tmpPos++] = a[rightPos++];

		// Copy tmpArray back
		for (int i = 0; i < numElements; i++, rightEnd--) {
			a[rightEnd] = tmpArray[rightEnd];
		}
	}

	/**
	 * Internal quick sort method that makes recursive calls. Uses
	 * median-of-three partitioning and a cutoff of 10
	 * 
	 * @param a
	 *            an array of Comparable items
	 * @param left
	 *            the left-most index of the sub-array.
	 * @param right
	 *            the right-most index of the sub-array.
	 */
	private static <T extends Comparable<? super T>> void quickSort(T[] a,
			int left, int right) {
		if (left + CUTOFF <= right) {
			T pivot = median3(a, left, right);

			// Begin partitioning
			int i = left, j = right - 1;
			for (;;) {
				while (a[++i].compareTo(pivot) < 0) {
				}
				while (a[--j].compareTo(pivot) > 0) {
				}
				if (i < j) {
					swapReferences(a, i, j);
				} else {
					break;
				}
			}

			swapReferences(a, i, right - 1); // Restore pivot

			quickSort(a, left, i - 1); // Sort small elements
			quickSort(a, i + 1, right);// Sort large elements
		} else
		// Do an insertion sort on the sub-array
		{
			insertionSort(a, left, right);
		}
	}

	private static <T extends Comparable<? super T>> T median3(T[] a, int left,
			int right) {
		int center = (left + right) / 2;
		if (a[center].compareTo(a[left]) < 0)
			swapReferences(a, left, center);
		if (a[right].compareTo(a[left]) < 0)
			swapReferences(a, left, right);
		if (a[right].compareTo(a[center]) < 0)
			swapReferences(a, center, right);

		// Place pivot at position right-1
		swapReferences(a, center, right - 1);
		return a[right - 1];
	}

	/**
	 * Internal insertion method
	 * 
	 * @param a
	 *            an array of Comparable items
	 * @param left
	 *            the left-most index of the array
	 * @param right
	 *            the right-most index of the array
	 */
	private static <T extends Comparable<? super T>> void insertionSort(T[] a,
			int left, int right) {
		if (left < right) {
			int j;

			for (int p = left + 1; p <= right; p++) {
				T tmp = a[p];
				for (j = p; j > left && tmp.compareTo(a[j - 1]) < 0; j--)
					a[j] = a[j - 1];
				a[j] = tmp;
			}
		}
	}

	/**
	 * Internal method: Swap the position of two elements of an array by
	 * referencing
	 * 
	 * @param a
	 *            an array for swapping the element
	 * @param i
	 *            the first element's index
	 * @param j
	 *            the second element's index
	 * @return the array after swapping
	 */
	private static <T> T[] swapReferences(T[] a, int i, int j) {
		T tmp = a[i];
		a[i] = a[j];
		a[j] = tmp;
		return a;
	}
	
	public static void main(String[] args){
		Integer[] ori=new Integer[]{32,1,45,63,76,8,3,6,8,9,2,4,56,788,934,5,4,3};
		long s1=System.nanoTime();
		SortUtil.bubbleSort(ori);
		System.out.println("bubleSort:"+(System.nanoTime()-s1));
		printArray(Arrays.asList(ori));
		
		Integer[] ori2=new Integer[]{32,1,45,63,76,8,3,6,8,9,2,4,56,788,934,5,4,3};
		long s2=System.nanoTime();
		SortUtil.insertionSort(ori2);
		System.out.println("insertionSort:"+(System.nanoTime()-s2));
		printArray(Arrays.asList(ori2));
		
		Integer[] ori3=new Integer[]{32,1,45,63,76,8,3,6,8,9,2,4,56,788,934,5,4,3};
		long s3=System.nanoTime();
		SortUtil.mergeSort(ori3);
		System.out.println("mergeSort:"+(System.nanoTime()-s3));
		printArray(Arrays.asList(ori3));
		
		Integer[] ori4=new Integer[]{32,1,45,63,76,8,3,6,8,9,2,4,56,788,934,5,4,3};
		long s4=System.nanoTime();
		SortUtil.heapSort(ori4);
		System.out.println("heapSort:"+(System.nanoTime()-s4));
		printArray(Arrays.asList(ori4));
		
		Integer[] ori5=new Integer[]{32,1,45,63,76,8,3,6,8,9,2,4,56,788,934,5,4,3};
		long s5=System.nanoTime();
		SortUtil.quickSort(ori5);
		System.out.println("quickSort:"+(System.nanoTime()-s5));
		printArray(Arrays.asList(ori5));
		
		Integer[] ori6=new Integer[]{32,1,45,63,76,8,3,6,8,9,2,4,56,788,934,5,4,3};
		long s6=System.nanoTime();
		SortUtil.selectionSort(ori6);
		System.out.println("selectionSort:"+(System.nanoTime()-s6));
		printArray(Arrays.asList(ori6));
		
		Integer[] ori7=new Integer[]{32,1,45,63,76,8,3,6,8,9,2,4,56,788,934,5,4,3};
		long s7=System.nanoTime();
		SortUtil.shellSort(ori7);
		System.out.println("shellSort:"+(System.nanoTime()-s7));
		printArray(Arrays.asList(ori7));
	}

	@SuppressWarnings("rawtypes")
	public static void printArray(List array){
		StringBuilder sb=new StringBuilder();
		for(Object o:array){
			sb.append(String.valueOf(o));
			sb.append(" ");
		}
		System.out.println(sb.toString());
	}
}