排序系列（五）---归并排序

 

//author:lilywangcn

public class MergeSort {

//private static int[] array=new int[]{10,30,20,4, 9,-1,6,15,12,8,0,20,4};

private static int[] array=new int[]{10,30,20,4,9,-1,6,15};

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

mergeSort(0,array.length-1);

}

public static void mergeSort(int left, int right){

if(left==right) return;

mergeSort(left,(left+right)/2);  //中间的值是(left+right)/2

mergeSort((right+left)/2+1,right);

int[] tmp=new int[right-left+1];  //存储临时归并的结果

int i=left,j=(right+left)/2+1,k=0;//开始归并

while(i<=(right+left)/2&&j<=right){

if(array[i]<=array[j]) tmp[k++]=array[i++];

else tmp[k++]=array[j++];

}

while(i>(right+left)/2&&j<=right){

tmp[k++]=array[j++];

}

while(j>right&&i<=(right+left)/2)

tmp[k++]=array[i++];

for(int m=0;m<tmp.length;m++){

array[left+m]=tmp[m];    //将临时归并结果拷贝回数组

}

print();  //一次归并后的结果

}

private static void print(){

for(int i=0;i<array.length;i++){

System.out.print(array[i]+" ");

}

System.out.println("");

}

 

}

算法复杂度：O(n*log2n),算法是稳定的。

//运行结果

10 30 20 4 9 -1 6 15 

10 30 4 20 9 -1 6 15 

4 10 20 30 9 -1 6 15 

4 10 20 30 -1 9 6 15 

4 10 20 30 -1 9 6 15 

4 10 20 30 -1 6 9 15 

-1 4 6 9 10 15 20 30