Java-归并排序

public void mergeSort(int[] a, int first, int last, int[] temp){

if(first<last){

int mid = (first+last)/2;

mergeSort(a,first,mid,temp);       //左边有序

mergeSort(a,mid+1,last,temp);   //右边有序

//把相邻两个有序的数组合并，形成一个新的有序数组

mergeArray(a,first,mid,last,temp);

}

}

private void mergeArray(int[] a, int first, int mid, int last, int[] temp) {

int i=first,m=mid;

int j=mid+1,n=last;

int count = 0;//记录这次合并了几个数

while(i<=m && j<=n){

if(a[i] <=a[j]){

temp[count++] = a[i++];

} else{

temp[count++] = a[j++];

}

}

while(i<=m){

temp[count++] = a[i++];

}

while(j<=n){

temp[count++] = a[j++];

}

//把临时数组排好序的部分拷贝回原始数组

for(int k=0; k<count; k++){

a[first+k] = temp[k];

}

}