数组排序: 几种排序算法

public class Sort {

	/**
	 * 选择排序
	 * 
	 * @param a
	 */
	public void selectSort(int[] a) {
		int index;
		int temp;
		int len = a.length;
		for (int i = 0; i < len - 1; i++) {
			index = 0;
			for (int j = 0; j < len - i; j++) {
				if (a[index] < a[j]) {
					index = j;
				}
			}
			temp = a[index];
			a[index] = a[len - i - 1];
			a[len - i - 1] = temp;
		}
	}

	/**
	 * 冒泡排序: 小至大
	 * 
	 * @param a
	 */
	public void bubbleSort(int[] a) {

		for (int j = 0; j < a.length; j++) {
			for (int i = 0; i < a.length - j - 1; i++) {
				if (a[i] > a[i + 1]) {
					// 使用异或换值
					// a[i+1] = a[i+1] ^ a[i] ;
					// a[i] = a[i+1] ^ a[i] ;
					// a[i+1] = a[i+1] ^ a[i] ;
					// 使用中间变量换值
					// int temp = a[i+1];
					// a[i+1] = a[i];
					// a[i] = temp;
					a[i + 1] = a[i + 1] + a[i];
					a[i] = a[i + 1] - a[i];
					a[i + 1] = a[i + 1] - a[i];
				}
			}
		}
	}

	/**
	 * 直接插入排序: 小至大
	 * 
	 * @param
	 */
	public void straightInsertSort(int[] a) {
		int temp;
		for (int i = 1; i < a.length; i++) {
			temp = a[i];
			for (int j = i - 1; j >= 0; j--) {
				if (a[j] > temp) {
					a[j + 1] = a[j];
				} else {
					a[j + 1] = temp;
					break;
				}
			}
		}
	}

	/**
	 * 与straightInsertShort原理差不多，只是在寻找插入点时使用了二分查找
	 * 
	 * @param a
	 */
	public void binaryInsertSort(int[] a) {

		for (int i = 1; i < a.length; i++) {
			int low = 0;
			int hight = i - 1;
			int temp = a[i];
			while (low <= hight) {
				int mid = (low + hight) / 2;
				if (a[mid] < temp) {
					low = mid + 1;
				} else {
					hight = mid - 1;
				}
			}
			for (int j = i - 1; j >= low; j--) {
				a[j + 1] = a[j];
			}
			a[low] = temp;
		}
	}

	/**
	 * 快速排序 ：小至大 思路： 选择一个基准元素，通过一趟扫描，（比大小）将待排序分成两个部分，然后对分好的两部分递归使用快排
	 * 
	 * @param a
	 * @param star
	 * @param end
	 */
	public void quickSort(int[] a, int star, int end) {

		int i = star;
		int j = end;
		int m = a[i];

		while (i < j) {
			while (a[j] > m && j > i) {
				j--;
			}
			if (j > i) {
				a[i] = a[j];
				i++;
			}
			while (a[i] < m && j > i) {
				i++;
			}
			if (j > i) {
				a[j] = a[i];
				j--;
			}
		}
		a[i] = m;

		if (i - 1 > star) {
			quickSort(a, star, i - 1);
		}
		if (i + 1 < end) {
			quickSort(a, i + 1, end);
		}
	}

	/**
	 * 堆排序
	 * 
	 * @param a
	 */
	public void heapSort(int[] a) {
		int k;
		int len = a.length;
		for (int i = 0; i < len - 1; i++) {

			k = createHeap(a, len - i - 1);
			swap(a, 0, len - i - 1);
		}
	}

	// 创建大根堆，取出最大值
	public int createHeap(int[] a, int lastIndex) {
		int k = 0;
		for (int i = (lastIndex - 1) / 2; i >= 0; i--) {
			// 从最后一个父节点开始，将其位置赋给 k
			k = i;
			while (2 * k + 1 <= lastIndex) {
				// 判断 k 父节点是否有右子节点
				int biggerIndex = 2 * k + 1;
				if (2 * k + 1 < lastIndex) {
					// 若有右子节点，取出大者
					if (a[2 * k + 1] < a[2 * k + 2]) {
						biggerIndex += 1;
					}
				}
				if (a[biggerIndex] > a[k]) {
					swap(a, biggerIndex, k);
					k = biggerIndex;
				} else {
					break;
				}
			}
		}
		return k;
	}

	// 换值
	public void swap(int[] a, int pos1, int pos2) {
		a[pos1] = a[pos1] + a[pos2];
		a[pos2] = a[pos1] - a[pos2];
		a[pos1] = a[pos1] - a[pos2];
	}
}