雞尾酒排序

雞尾酒排序（Cocktail shaker sort），亦為定向冒泡排序，雞尾酒攪拌排序，攪拌排序（也可以視作選擇排序的一種變形），漣漪排序，來回排序或快樂小時排序，是冒泡排序的一種變形。此演演算法與冒泡排序的不同處在於排序時是以雙向在序列中進行排序。

## 偽代碼

將一個序列由小到大進行排序：

```
'''function''' cocktail_sort(list, list_length){ <span style="color:green">// the first element of list has index 0</span>
    bottom = 0;
    top = list_length - 1;
    swapped = true; 
    '''while'''(swapped == true) <span style="color:green">// if no elements have been swapped, then the list is sorted</span>
    {
        swapped = false; 
        '''for'''(i = bottom; i < top; i = i + 1)
        {
            '''if'''(list[i] > list[i + 1])  <span style="color:green">// test whether the two elements are in the correct order</span>
            {
                swap(list[i], list[i + 1]); <span style="color:green">// let the two elements change places</span>
                swapped = true;
            }
        }
        <span style="color:green">// decreases top the because the element with the largest value in the unsorted
        // part of the list is now on the position top </span>
        top = top - 1; 
        '''for'''(i = top; i > bottom; i = i - 1)
        {
            '''if'''(list[i] < list[i - 1]) 
            {
                swap(list[i], list[i - 1]);
                swapped = true;
            }
        }
        <span style="color:green">// increases bottom because the element with the smallest value in the unsorted 
        // part of the list is now on the position bottom </span>
        bottom = bottom + 1;  
    }
}
```

## 與冒泡排序不同的地方

雞尾酒排序等於是冒泡排序的輕微變形。不同的地方在於從低到高然後從高到低，而冒泡排序則僅從低到高去比較序列裡的每個元素。他可以得到比冒泡排序稍微好一點的效能，原因是冒泡排序只從一個方向進行比對（由低到高），每次循環只移動一個項目。

以序列（2,3,4,5,1）為例，雞尾酒排序只需要訪問一次序列就可以完成排序，但如果使用冒泡排序則需要四次。但是在亂數序列的狀態下，雞尾酒排序與冒泡排序的效率與其他眾多排序算法相比均比較低。

## 實作範例

### C語言

```c
void cocktail_sort(int arr[], int len) {
	int i, left = 0, right = len - 1;
	int temp;
	while (left < right) {
		for (i = left; i < right; i++)
			if (arr[i] > arr[i + 1]) {
				temp = arr[i];
				arr[i] = arr[i + 1];
				arr[i + 1] = temp;
			}
		right--;
		for (i = right; i > left; i--)
			if (arr[i - 1] > arr[i]) {
				temp = arr[i];
				arr[i] = arr[i - 1];
				arr[i - 1] = temp;
			}
		left++;
	}
}
```

### C++

```cpp
template<typename T> //整數或浮點數皆可使用,若要使用物件(class)時必須設定大於(>)的運算子功能
void cocktail_sort(T arr[], int len) {
	int j, left = 0, right = len - 1;
	while (left < right) {
		for (j = left; j < right; j++)
			if (arr[j] > arr[j + 1])
				swap(arr[j], arr[j + 1]);
		right--;
		for (j = right; j > left; j--)
			if (arr[j - 1] > arr[j])
				swap(arr[j - 1], arr[j]);
		left++;
	}
}
```

### Rust

```Rust
fn cocktail_sort<T: PartialOrd>(arr: &mut [T]) {
    let mut bottom: usize = 0;
    let mut top = arr.len() - 1;
    let mut swapped = true;

    while swapped {
        swapped = false;
        for i in bottom..top {
            if arr[i] > arr[i+1] {
                arr.swap(i, i+1);
                swapped = true;
            }
        }

        top -= 1;
        for j in ((bottom + 1)..=top).rev() {
            if arr[j] < arr[j - 1] {
                arr.swap(j, j - 1);
                swapped = true;
            }
        }
        bottom += 1;
    }
}
```

### JAVA

```java
public static void cocktail_sort(int[] arr) {	
	int i, left = 0, right = arr.length - 1;
	int temp;
	while (left < right) {
		for (i = left; i < right; i++)
			if (arr[i] > arr[i + 1]) {
				temp = arr[i];
				arr[i] = arr[i + 1];
				arr[i + 1] = temp;
			}
		right--;
		for (i = right; i > left; i--)
			if (arr[i - 1] > arr[i]) {
				temp = arr[i];
				arr[i] = arr[i - 1];
				arr[i - 1] = temp;
			}
		left++;
	}
}
```

### JavaScript

```javascript
Array.prototype.cocktail_sort = function() {
	var i, left = 0, right = this.length - 1;
	var temp;
	while (left < right) {
		for (i = left; i < right; i++)
			if (this[i] > this[i + 1]) {
				temp = this[i];
				this[i] = this[i + 1];
				this[i + 1] = temp;
			}
		right--;
		for (i = right; i > left; i--)
			if (this[i - 1] > this[i]) {
				temp = this[i];
				this[i] = this[i - 1];
				this[i - 1] = temp;
			}
		left++;
	}
};
```

### PHP

```php
function swap(&$x, &$y) {
	$t = $x;
	$x = $y;
	$y = $t;
}
function cocktail_sort(&$arr) {//php的陣列視為基本型別，所以必須用傳參才能修改原陣列
	$left = 0;
	$right = count($arr) - 1;
	while ($left < $right) {
		for ($j = $left; $j < $right; $j++)
			if ($arr[$j] > $arr[$j + 1])
				swap($arr[$j], $arr[$j + 1]);
		$right--;
		for ($j = $right; $j > $left; $j--)
			if ($arr[$j - 1] > $arr[$j])
				swap($arr[$j - 1], $arr[$j]);
		$left++;
	}
}
```

### Python 2.7

```python3
def cocktail_sort(l):
    l_len = len(l)
    for i in range(l_len, 0, -1):
        rem_i_l_len = abs(i - l_len)
        isNeedContinue = False
        obverse_count = len(l[rem_i_l_len : i-1])
        reverse_count = len(l[rem_i_l_len + 1 : i-1])
        
        for j in range(obverse_count):
            if l[j] > l[j + 1]:
                l[j], l[j + 1] = l[j + 1], l[j]
                isNeedContinue = True
        # you can print this to observe the whole process
        # print l
        
        for j in range(reverse_count, 0, -1):
            if l[j] < l[j - 1]:
                l[j], l[j - 1] = l[j - 1], l[j]
                isNeedContinue = True
        # you can print this to observe the whole process
        # print l
        
        if isNeedContinue:
            continue
        else:
            return
  
        
if __name__ == '__main__':
    sample_list = [6,5,4,3,2,100]
    cocktail_sort(sample_list)
    print(sample_list)
```

### Python 3.10

```python3
def cocktail_sort(arr: list, bottom: int = None, top: int = None):
    if not bottom and not top:
        bottom, top = 0, len(arr) - 1

    if bottom == top or bottom > top:
        return

    swapped: bool = False
    for i in range(bottom, top):
        if arr[i] > arr[i + 1]:
            arr[i + 1], arr[i] = arr[i], arr[i + 1]
            swapped = True

    for i in range(top - 1, bottom, -1):
        if arr[i] < arr[i - 1]:
            arr[i - 1], arr[i] = arr[i], arr[i - 1]
            swapped = True

    if not swapped:
        return

    cocktail_sort(arr, bottom + 1, top - 1)

if __name__ == '__main__':
    sample_list = [3, 7, 5, 1, 6, 4, 8, 2]
    cocktail_sort(sample_list)
    print(sample_list)
```

### Golang

```go
func cocktailSort(arr []int) {
	left := 0
	right := len(arr) - 1

	for left < right {
		for i := left; i < right; i++ {
			if arr[i] > arr[i+1] {
				arr[i], arr[i+1] = arr[i+1], arr[i]
			}
		}
		right--

		for i := right; i > left; i-- {
			if arr[i-1] > arr[i] {
				arr[i-1], arr[i] = arr[i], arr[i-1]
			}
		}
		left++
	}
}
```

### Julia (程式語言)

```julia
# Julia Sample : CocktailSort

function CocktailSort(A)
	isordered, lo, hi  = false, 1, length(A)
 
	while !isordered && hi > lo
		isordered = true
		
		for i=lo+1:hi
			if A[i] < A[i-1]
				A[i-1], A[i] = A[i], A[i-1]
				isordered = false
			end
		end
		
		hi -= 1
		
		if isordered || hi ≤ lo 
			break 
		end

		for i in hi:-1:lo+1
			if A[i-1] > A[i]
				A[i-1], A[i] = A[i], A[i-1]
				isordered = false
			end
		end
		lo += 1
	end
	return A
end

# Main Code
A = [16,586,1,31,354,43,3]
println(A)                      # Original Array
println(CocktailSort(A)) 		# Cocktail Sort Array
```

## 複雜度

雞尾酒排序最糟或是平均所花費的次數都是$O(n^2)$，但如果序列在一開始已經大部分排序過的話，會接近$O(n)$。

## 外部連結

- Java source code and an animated demo of cocktail sort (called bi-directional bubble sort) and several other algorithms
- Implementations of cocktail sort in several different programming languages