選擇排序法
public class SelectionSort{
private SelectionSort(){}
public static void sort(Comparable[] arr){
int n = arr.length;
for(int i = 0 ;i < n; i++){
int minIndex = i;
for(int j = i+1 ; j < n; j++){
if(arr[minIndex].compareTo(arr[j])>0){
minIndex = j;
}
}
swap(arr,minIndex,j);
}
}
private static void swap(Object[] arr,int index1,int index2){
Object o = arr[index1];
arr[index1] = arr[index2];
arr[index2] = o;
}
}
寫法1
public class BubbleSort {
private BubbleSort(){}
public static void sort(Comparable[] arr){
int n = arr.length;
boolean swapped = false;
do{
swapped = false;
for( int i = 1 ; i < n ; i ++ )
if( arr[i-1].compareTo(arr[i]) > 0 ){
swap( arr , i-1 , i );
swapped = true;
}
n --;
}while(swapped);
}
private static void swap(Object[] arr, int i, int j) {
Object t = arr[i];
arr[i] = arr[j];
arr[j] = t;
}
}
改進寫法
public class BubbleSort2 {
private BubbleSort2(){}
public static void sort(Comparable[] arr){
int n = arr.length;
int newn;
do{
newn = 0;
for( int i = 1 ; i < n ; i ++ )
if( arr[i-1].compareTo(arr[i]) > 0 ){
swap( arr , i-1 , i );
newn = i;
}
n = newn;
}while(newn > 0);
}
private static void swap(Object[] arr, int i, int j) {
Object t = arr[i];
arr[i] = arr[j];
arr[j] = t;
}
}
插入排序法 Insertion Sort
public class InsertionSort{
private InsertionSort(){}
public static void sort(Comparable[] arr){
int n = arr.length;
for(int i = 0; i < n ; i++){
Comparable comparable = arr[i];
int j = i;
for(;j > 0 && arr[j-1].compareTo(comparable)>0 ;j--){
arr[j] = arr[j-1];
}
arr[j] = comparable;
}
}
private static void swap(Object[] arr,int index1, int index2){
Object object = arr[index1];
arr[index1] = arr[index2];
arr[index2] = object;
}
}
希爾排序 ShellSort
- 希爾排序就是在InsertionSort改進而來的。只是設置了交換步長,當步長逐漸縮小唯一的時候,就InsertionSort,只是此時,該數列基本有序,此時插入排序的性能十分優異。
- 時間複雜度O(n^1.5)
public class ShellSort{
private ShellSort() {
}
public static void sort(Comparable[] arr){
int n = arr.lenght;
int h = 1;
while(h < n/3) h = h*3+1;
while(h >= 1){
for(int i = h ; i < n ; i++){
Comparable comparable = arr[i];
int j = i;
for(;j>=h && comparable.compareTo(arr[j-h])<0;j -= h){
arr[j] = arr[j - h];
}
arr[j] = comparable;
}
h /= 3;
}
}
}