八大排序算法之归并排序

package java面试宝典;

import java.util.Arrays;

public class 归并排序 {
	public static void main(String[] args) {
		int[] a={6,9,3,5,7,1,8,0,2,4};
		System.out.println(Arrays.toString(a));
		mergeSort(a,0,a.length-1);
		System.out.println(Arrays.toString(a));
		
	}
	public static void mergeSort(int[] a,int p,int r){
		if(p<r){
			int q=(p+r)/2;
			mergeSort(a, p, q);
			mergeSort(a, q+1, r);
			merge(a, p, q, r);
		}
	}
	public static void merge(int[] a,int p,int q,int r){
		int[] L=new int[q-p+1];
		int[] R=new int[r-q];
		int k=p;
		int i=0;
		int j=0;
		for (i = 0; i < L.length; i++) {
			L[i]=a[k++];
		}
		for (i = 0,k=q+1; i < R.length; i++) {
			R[i]=a[k++];
		}
		i=0;
		j=0;
		k=p;
		while(i<L.length&&j<R.length){
			if(L[i]<R[j]){
				a[k++]=L[i++];
			}else{
				a[k++]=R[j++];
			}
		}
		while(i<L.length){
			a[k++]=L[i++];
		}
		while(j<R.length){
			a[k++]=R[j++];
		}
	}
}