归并排序

public class MergeSort {

	private static int[] b;
	
	public static void mergeSort(int[] a){
		if(a == null) return;
		b = new int[a.length];
		merge(a, 0, a.length-1);
	}
	
	private static void merge(int[] a, int start, int end){
		if(start >= end){
			return;
		}
		int mid = (start+end)/2;
		merge(a, start, mid);
		merge(a, mid+1, end);
		int i = start;
		int j = mid+1;
		int k = 0;
		while((i<=mid) && (j<=end)){
			if(a[i] < a[j]){
				b[k] = a[i];
				i++;
			}else{
				b[k] = a[j];
				j++;
			}
			k++;
		}
		if(i > mid){
			while(j<=end){
				b[k] = a[j];
				j++;
				k++;
			}
		}
		if(j > end){
			while(i<=mid){
				b[k] = a[i];
				i++;
				k++;
			}
		}
		for(int m=start; m<=end; m++){
			a[m] = b[m-start];
		}
	}
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		int[] a = {7,2,4,8,3,5,1,9,0,6};
		MergeSort.mergeSort(a);
		Tools.printArray(a);

	}

}