排序—归并排序

归并排序算法可以递归的描述为：算法将数组分为两半，对每部分递归地应用归并排序。在两部分都排好序后，对它们进行归并。

package ss.sort;
/**
 * 归并排序
 * @author zhangss 2016-4-26 14:06:04
 * */
public class MergeSort {
	
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		int[] list = {2, 3, 2, 5, 6, 1, -2, 3, 4, 14, 12};
		mergeSort(list);
		for(int temp : list)
			System.out.println(temp);
	}
	public static void mergeSort(int[] list){
		if(list.length>1){
			// marge sort the first half
			int[] firstHalf = new int[list.length/2];
			System.arraycopy(list, 0, firstHalf, 0, list.length/2);
			mergeSort(firstHalf);
			
			// marge sort the secode half
			int secondHalfLength = list.length - list.length/2;
			int[] secondHalf = new int[secondHalfLength];
			System.arraycopy(list, list.length/2, secondHalf, 0, secondHalfLength);
			mergeSort(secondHalf);
			
			//Merge firstHalf with secondHalf
			int[] temp = merge(firstHalf, secondHalf);
			System.arraycopy(temp, 0, list, 0, temp.length);
		}
	}
	
	/** Merge two sorted lists */
	private static int[] merge(int[] list1, int[] list2){
		int[] temp = new int[list1.length + list2.length];
		
		int current1 = 0;    // Current index in list1
		int current2 = 0;    // Current index in list2 
		int current3 = 0;    // Current index in temp
		
		while(current1<list1.length && current2 < list2.length){
			if(list1[current1] < list2[current2]){
				temp[current3++] = list1[current1++];
			}else{
				temp[current3++] = list2[current2++];
			}
		}
		
		while(current1 < list1.length){
			temp[current3++] = list1[current1++];
		}
		
		while(current2 < list2.length){
			temp[current3++] = list2[current2++];
		}
		return temp;
	}
}