快速排序
2010-12-07 10:41
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public static Integer CUTOFF = 10;
/**
* 交换位置
*/
public static <AnyType extends Comparable<? super AnyType>> void swapReferences(AnyType [] a,int left,int right){
AnyType temp ;
temp = a[ left ];
a[ left ] = a[ right ];
a[ right ] = temp;
}
/**
* 插入排序
*/
public static <AnyType extends Comparable<? super AnyType>> void insertSort(AnyType [] a){
int j;
for(int p = 1; p < a.length; p++){
AnyType temp = a[ p ];
for(j = p; j > 0 && temp.compareTo(a[ j - 1 ]) < 0;j--){
a[ j ] = a[ j - 1 ];
}
a[ j ] = temp;
}
}
/**
* Return median of left,center, and right .
* Order these and hide the pivot
*/
public static <AnyType extends Comparable<? super AnyType>> AnyType median3(AnyType [] a,int left,int right){
int center = ( left + right ) / 2;
if(a[ center ].compareTo(a[ left ]) < 0){
swapReferences(a,left,center);
}
if(a[ right ].compareTo(a[ left]) < 0){
swapReferences(a,left,right);
}
if(a[ right ].compareTo(a[ center ]) < 0){
swapReferences(a,center,right);
}
//Place pivot at position right - 1
swapReferences(a,center,right - 1);
return a[right - 1];
}
/**
* quickSort that makes recursive calls
* CUTOFF 为截止的个数,书上说经研究,在数量较小的情况下,插入排序比快排的效率高,所以在数量少的情况下使用插入排序,
* CUTOFF值为10
*/
public static <AnyType extends Comparable<? super AnyType>> void quickSort(AnyType a[],int left,int right){
if(left + CUTOFF < right){
AnyType pivot = median3(a,left,right);
//Begin partitioning
int i = left,j = right - 1;
for(;;){
while(a[ ++i ].compareTo( pivot ) < 0){}
while(a[ --j ].compareTo( pivot ) < 0){}
if(i < j)
swapReferences( a, i, j);
else
break;
}
swapReferences(a, i, right - 1);//restore pivot
quickSort(a, left, i - 1);
quickSort(a, i + 1, right);
}
else{
insertSort(a);
}
}
/**
* 交换位置
*/
public static <AnyType extends Comparable<? super AnyType>> void swapReferences(AnyType [] a,int left,int right){
AnyType temp ;
temp = a[ left ];
a[ left ] = a[ right ];
a[ right ] = temp;
}
/**
* 插入排序
*/
public static <AnyType extends Comparable<? super AnyType>> void insertSort(AnyType [] a){
int j;
for(int p = 1; p < a.length; p++){
AnyType temp = a[ p ];
for(j = p; j > 0 && temp.compareTo(a[ j - 1 ]) < 0;j--){
a[ j ] = a[ j - 1 ];
}
a[ j ] = temp;
}
}
/**
* Return median of left,center, and right .
* Order these and hide the pivot
*/
public static <AnyType extends Comparable<? super AnyType>> AnyType median3(AnyType [] a,int left,int right){
int center = ( left + right ) / 2;
if(a[ center ].compareTo(a[ left ]) < 0){
swapReferences(a,left,center);
}
if(a[ right ].compareTo(a[ left]) < 0){
swapReferences(a,left,right);
}
if(a[ right ].compareTo(a[ center ]) < 0){
swapReferences(a,center,right);
}
//Place pivot at position right - 1
swapReferences(a,center,right - 1);
return a[right - 1];
}
/**
* quickSort that makes recursive calls
* CUTOFF 为截止的个数,书上说经研究,在数量较小的情况下,插入排序比快排的效率高,所以在数量少的情况下使用插入排序,
* CUTOFF值为10
*/
public static <AnyType extends Comparable<? super AnyType>> void quickSort(AnyType a[],int left,int right){
if(left + CUTOFF < right){
AnyType pivot = median3(a,left,right);
//Begin partitioning
int i = left,j = right - 1;
for(;;){
while(a[ ++i ].compareTo( pivot ) < 0){}
while(a[ --j ].compareTo( pivot ) < 0){}
if(i < j)
swapReferences( a, i, j);
else
break;
}
swapReferences(a, i, right - 1);//restore pivot
quickSort(a, left, i - 1);
quickSort(a, i + 1, right);
}
else{
insertSort(a);
}
}
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