选择排序

选择排序算法通过从未排序部分重复查找最小元素(考虑升序)并将其放在开头来对数组进行排序。该算法在给定数组中维护两个子数组。

1)已排序的子数组。
2)未排序的剩余子数组。

在选择排序的每次迭代中，都会从未排序的子数组中选取最小元素(考虑升序)并将其移至已排序的子数组。

以下示例说明了上述步骤：

arr[] = 64 25 12 22 11

// Find the minimum element in arr[0...4]
// and place it at beginning
11 25 12 22 64

// Find the minimum element in arr[1...4]
// and place it at beginning of arr[1...4]
11 12 25 22 64

// Find the minimum element in arr[2...4]
// and place it at beginning of arr[2...4]
11 12 22 25 64

// Find the minimum element in arr[3...4]
// and place it at beginning of arr[3...4]
11 12 22 25 64 

选择排序流程图：

C++

// C++ program for implementation of selection sort 
#include 
using namespace std;
  
void swap(int *xp, int *yp) 
{ 
    int temp = *xp; 
    *xp = *yp; 
    *yp = temp; 
} 
  
void selectionSort(int arr[], int n) 
{ 
    int i, j, min_idx; 
  
    // One by one move boundary of unsorted subarray 
    for (i = 0; i < n-1; i++) 
    { 
        // Find the minimum element in unsorted array 
        min_idx = i; 
        for (j = i+1; j < n; j++) 
        if (arr[j] < arr[min_idx]) 
            min_idx = j; 
  
        // Swap the found minimum element with the first element 
        swap(&arr[min_idx], &arr[i]); 
    } 
} 
  
/* Function to print an array */
void printArray(int arr[], int size) 
{ 
    int i; 
    for (i=0; i < size; i++) 
        cout << arr[i] << " "; 
    cout << endl; 
} 
  
// Driver program to test above functions 
int main() 
{ 
    int arr[] = {64, 25, 12, 22, 11}; 
    int n = sizeof(arr)/sizeof(arr[0]); 
    selectionSort(arr, n); 
    cout << "Sorted array: \n"; 
    printArray(arr, n); 
    return 0; 
} 
  
// This is code is contributed by rathbhupendra

C

// C program for implementation of selection sort
#include 
  
void swap(int *xp, int *yp)
{
    int temp = *xp;
    *xp = *yp;
    *yp = temp;
}
  
void selectionSort(int arr[], int n)
{
    int i, j, min_idx;
  
    // One by one move boundary of unsorted subarray
    for (i = 0; i < n-1; i++)
    {
        // Find the minimum element in unsorted array
        min_idx = i;
        for (j = i+1; j < n; j++)
          if (arr[j] < arr[min_idx])
            min_idx = j;
  
        // Swap the found minimum element with the first element
        swap(&arr[min_idx], &arr[i]);
    }
}
  
/* Function to print an array */
void printArray(int arr[], int size)
{
    int i;
    for (i=0; i < size; i++)
        printf("%d ", arr[i]);
    printf("\n");
}
  
// Driver program to test above functions
int main()
{
    int arr[] = {64, 25, 12, 22, 11};
    int n = sizeof(arr)/sizeof(arr[0]);
    selectionSort(arr, n);
    printf("Sorted array: \n");
    printArray(arr, n);
    return 0;
}

Python

# Python program for implementation of Selection
# Sort
import sys
A = [64, 25, 12, 22, 11]
  
# Traverse through all array elements
for i in range(len(A)):
      
    # Find the minimum element in remaining 
    # unsorted array
    min_idx = i
    for j in range(i+1, len(A)):
        if A[min_idx] > A[j]:
            min_idx = j
              
    # Swap the found minimum element with 
    # the first element        
    A[i], A[min_idx] = A[min_idx], A[i]
  
# Driver code to test above
print ("Sorted array")
for i in range(len(A)):
    print("%d" %A[i]),

Java

// Java program for implementation of Selection Sort
class SelectionSort
{
    void sort(int arr[])
    {
        int n = arr.length;
  
        // One by one move boundary of unsorted subarray
        for (int i = 0; i < n-1; i++)
        {
            // Find the minimum element in unsorted array
            int min_idx = i;
            for (int j = i+1; j < n; j++)
                if (arr[j] < arr[min_idx])
                    min_idx = j;
  
            // Swap the found minimum element with the first
            // element
            int temp = arr[min_idx];
            arr[min_idx] = arr[i];
            arr[i] = temp;
        }
    }
  
    // Prints the array
    void printArray(int arr[])
    {
        int n = arr.length;
        for (int i=0; i

---

C#

// C# program for implementation 
// of Selection Sort
using System;
  
class GFG
{ 
    static void sort(int []arr)
    {
        int n = arr.Length;
  
        // One by one move boundary of unsorted subarray
        for (int i = 0; i < n - 1; i++)
        {
            // Find the minimum element in unsorted array
            int min_idx = i;
            for (int j = i + 1; j < n; j++)
                if (arr[j] < arr[min_idx])
                    min_idx = j;
  
            // Swap the found minimum element with the first
            // element
            int temp = arr[min_idx];
            arr[min_idx] = arr[i];
            arr[i] = temp;
        }
    }
  
    // Prints the array
    static void printArray(int []arr)
    {
        int n = arr.Length;
        for (int i=0; i

---

PHP

 $arr[$low])
        {
            $tmp = $arr[$i];
            $arr[$i] = $arr[$low];
            $arr[$low] = $tmp;
        }
    }
}
  
// Driver Code
$arr = array(64, 25, 12, 22, 11);
$len = count($arr);
selection_sort($arr, $len);
echo "Sorted array : \n"; 
  
for ($i = 0; $i < $len; $i++) 
    echo $arr[$i] . " "; 
  
// This code is contributed 
// by Deepika Gupta. 
?>

输出：

Sorted array: 
11 12 22 25 64

时间复杂度： O(n ² )，因为有两个嵌套循环。

辅助空间： O(1)
关于选择排序的好处是，它进行的交换不超过O(n)，并且在内存写入是一项昂贵的操作时很有用。

锻炼 ：
使用选择排序对字符串数组进行排序

稳定性：默认实现不稳定。但是，可以使其稳定。有关详细信息，请参见稳定选择排序。

就地：是的，它不需要额外的空间。