改进线性搜索技术

线性搜索或顺序搜索是一种在列表中查找元素的方法。它依次检查列表的每个元素，直到找到匹配项或搜索了整个列表。可以看出，当搜索一个关键元素时，就有可能一次又一次地搜索相同的关键元素。

目标是如果再次搜索相同的元素，则操作必须花费更少的时间。因此，在这种情况下，可以使用以下两种方法来改进线性搜索：

1. 换位
2. 移到前面

换位：

在转置中，如果找到关键元素，则将其交换到索引之前的元素以增加特定关键字的搜索次数，搜索操作也会优化并不断将元素移动到数组的开头搜索时间复杂度将是恒定时间。

例如：如果数组arr[]是 {2, 5, 7, 1, 6, 4, 5, 8, 3, 7} 并且让要搜索的键是 4，那么下面是步骤：

• 搜索键4 后，在 6 次比较后在给定数组的索引 5处找到该元素。现在在转置后，数组变为 {2, 5, 7, 1, 4, 6, 5, 8, 3, 7} 即，值为 4 的键位于索引 4 处。
• 再次搜索键4 后，在 6 次比较后在给定数组的索引 4处找到该元素。现在在转置后，数组变为 {2, 5, 7, 4, 1, 6, 5, 8, 3, 7} 即，值为 4 的键位于索引 3 处。
• 如果要查找的元素不在第一个索引处，则上述过程将继续，直到任何键到达数组的前面。

下面是上述算法的实现：

C

// C program for transposition to
// improve the Linear Search Algorithm
#include 
 
// Structure of the array
struct Array {
 
    int A[10];
    int size;
    int length;
};
 
// Function to print the array element
void Display(struct Array arr)
{
    int i;
 
    // Traverse the array arr[]
    for (i = 0; i < arr.length; i++) {
        printf("%d ", arr.A[i]);
    }
    printf("\n");
}
 
// Function that swaps two elements
// at different addresses
void swap(int* x, int* y)
{
    // Store the value store at
    // x in a variable temp
    int temp = *x;
 
    // Swapping of value
    *x = *y;
    *y = temp;
}
 
// Function that performs the Linear
// Search Transposition
int LinearSearchTransposition(
    struct Array* arr, int key)
{
    int i;
 
    // Traverse the array
    for (i = 0; i < arr->length; i++) {
 
        // If key is found, then swap
        // the element with it's
        // previous index
        if (key == arr->A[i]) {
 
            // If key is first element
            if (i == 0)
                return i;
 
            swap(&arr->A[i],
                 &arr->A[i - 1]);
 
            return i;
        }
    }
    return -1;
}
 
// Driver Code
int main()
{
    // Given array arr[]
    struct Array arr
        = { { 2, 23, 14, 5, 6, 9, 8, 12 },
            10,
            8 };
 
    printf("Elements before Linear"
           " Search Transposition: ");
 
    // Function Call for displaying
    // the array arr[]
    Display(arr);
 
    // Function Call for transposition
    LinearSearchTransposition(&arr, 14);
 
    printf("Elements after Linear"
           " Search Transposition: ");
 
    // Function Call for displaying
    // the array arr[]
    Display(arr);
    return 0;
}

Java

// Java program for transposition
// to improve the Linear Search
// Algorithm
class GFG{
 
// Structure of the
// array
static class Array
{
  int []A = new int[10];
  int size;
  int length;
  Array(int []A, int size,
        int length)
  {
    this.A = A;
    this.size = size;
    this.length = length;
  }
};
 
// Function to print the
// array element
static void Display(Array arr)
{
  int i;
 
  // Traverse the array arr[]
  for (i = 0; i < arr.length; i++)
  {
    System.out.printf("%d ",
                      arr.A[i]);
  }
  System.out.printf("\n");
}
 
// Function that performs the Linear
// Search Transposition
static int LinearSearchTransposition(Array arr,
                                     int key)
{
  int i;
 
  // Traverse the array
  for (i = 0; i < arr.length; i++)
  {
    // If key is found, then swap
    // the element with it's
    // previous index
    if (key == arr.A[i])
    {
      // If key is first element
      if (i == 0)
        return i;
      int temp = arr.A[i];
      arr.A[i] = arr.A[i - 1];
      arr.A[i - 1] = temp;
      return i;
    }
  }
  return -1;
}
 
// Driver Code
public static void main(String[] args)
{
  // Given array arr[]
  int tempArr[] = {2, 23, 14, 5,
                   6, 9, 8, 12};
  Array arr = new Array(tempArr,
                        10, 8);
 
  System.out.printf("Elements before Linear" +
                    " Search Transposition: ");
 
  // Function Call for displaying
  // the array arr[]
  Display(arr);
 
  // Function Call for transposition
  LinearSearchTransposition(arr, 14);
 
  System.out.printf("Elements after Linear" +
                    " Search Transposition: ");
 
  // Function Call for displaying
  // the array arr[]
  Display(arr);
}
}
 
// This code is contributed by Princi Singh

C#

// C# program for transposition
// to improve the Linear Search
// Algorithm
using System;
 
class GFG{
 
// Structure of the
// array
public class Array
{
    public int []A = new int[10];
    public int size;
    public int length;
     
    public Array(int []A, int size,
                 int length)
    {
        this.A = A;
        this.size = size;
        this.length = length;
    }
};
 
// Function to print the
// array element
static void Display(Array arr)
{
    int i;
     
    // Traverse the array []arr
    for(i = 0; i < arr.length; i++)
    {
        Console.Write(arr.A[i] + " ");
    }
    Console.Write("\n");
}
 
// Function that performs the Linear
// Search Transposition
static int LinearSearchTransposition(Array arr,
                                     int key)
{
    int i;
     
    // Traverse the array
    for(i = 0; i < arr.length; i++)
    {
         
        // If key is found, then swap
        // the element with it's
        // previous index
        if (key == arr.A[i])
        {
             
            // If key is first element
            if (i == 0)
                return i;
                 
            int temp = arr.A[i];
            arr.A[i] = arr.A[i - 1];
            arr.A[i - 1] = temp;
            return i;
        }
    }
    return -1;
}
 
// Driver Code
public static void Main(String[] args)
{
     
    // Given array []arr
    int []tempArr = { 2, 23, 14, 5,
                      6, 9, 8, 12 };
    Array arr = new Array(tempArr, 10, 8);
     
    Console.Write("Elements before Linear " +
                  "Search Transposition: ");
     
    // Function Call for displaying
    // the array []arr
    Display(arr);
     
    // Function Call for transposition
    LinearSearchTransposition(arr, 14);
     
    Console.Write("Elements after Linear " +
                  "Search Transposition: ");
     
    // Function Call for displaying
    // the array []arr
    Display(arr);
}
}
 
// This code is contributed by Amit Katiyar

输出：
线性搜索换位前的元素：2 23 14 5 6 9 8 12
线性搜索换位后的元素：2 14 23 5 6 9 8 12

移到前面/头部：

在该方法中，如果找到关键元素，则直接将其与索引0交换，这样下一次连续搜索相同关键元素的操作为O(1) ，即常数时间。

例如：如果数组arr[]是 {2, 5, 7, 1, 6, 4, 5, 8, 3, 7} 并且让要搜索的键是 4，那么下面是步骤：

• 搜索键4 后，在 6 次比较后在给定数组的索引 5处找到该元素。现在移到前面操作后，数组变为 {4, 2, 5, 7, 1, 6, 5, 8, 3, 7} 即值为 4 的键位于索引 0 处。
• 再次搜索键4 后，在给定数组的索引 0处找到元素，这减少了整个数组的搜索空间。

C

// C program to implement the move to
// front to optimized Linear Search
#include 
 
// Structure of the array
struct Array {
 
    int A[10];
    int size;
    int length;
};
 
// Function to print the array element
void Display(struct Array arr)
{
    int i;
 
    // Traverse the array arr[]
    for (i = 0; i < arr.length; i++) {
        printf("%d ", arr.A[i]);
    }
    printf("\n");
}
 
// Function that swaps two elements
// at different addresses
void swap(int* x, int* y)
{
    // Store the value store at
    // x in a variable temp
    int temp = *x;
 
    // Swapping of value
    *x = *y;
    *y = temp;
}
 
// Function that performs the move to
// front operation for Linear Search
int LinearSearchMoveToFront(
    struct Array* arr, int key)
{
    int i;
 
    // Traverse the array
    for (i = 0; i < arr->length; i++) {
 
        // If key is found, then swap
        // the element with 0-th index
        if (key == arr->A[i]) {
            swap(&arr->A[i], &arr->A[0]);
            return i;
        }
    }
    return -1;
}
 
// Driver code
int main()
{
    // Given array arr[]
    struct Array arr
        = { { 2, 23, 14, 5, 6, 9, 8, 12 },
            10,
            8 };
 
    printf("Elements before Linear"
           " Search Move To Front: ");
 
    // Function Call for displaying
    // the array arr[]
    Display(arr);
 
    // Function Call for Move to
    // front operation
    LinearSearchMoveToFront(&arr, 14);
 
    printf("Elements after Linear"
           " Search Move To Front: ");
 
    // Function Call for displaying
    // the array arr[]
    Display(arr);
    return 0;
}

Java

// Java program to implement
// the move to front to optimized
// Linear Search
class GFG{
 
// Structure of the array
static class Array
{
  int []A = new int[10];
  int size;
  int length;
  Array(int []A, int size,
        int length)
  {
    this.A = A;
    this.size = size;
    this.length = length;
  }
};
 
// Function to print the
// array element
static void Display(Array arr)
{
  int i;
 
  // Traverse the array arr[]
  for (i = 0;
       i < arr.length; i++)
  {
    System.out.printf("%d ", arr.A[i]);
  }
  System.out.printf("\n");
}
 
// Function that performs the
// move to front operation for
// Linear Search
static int LinearSearchMoveToFront(Array arr,
                                   int key)
{
  int i;
 
  // Traverse the array
  for (i = 0; i < arr.length; i++)
  {
    // If key is found, then swap
    // the element with 0-th index
    if (key == arr.A[i])
    {
      int temp = arr.A[i];
      arr.A[i] = arr.A[0];
      arr.A[0] = temp;
      return i;
    }
  }
  return -1;
}
 
// Driver code
public static void main(String[] args)
{
  // Given array arr[]
  int a[] = {2, 23, 14, 5,
             6, 9, 8, 12 };
  Array arr = new Array(a, 10, 8);
 
  System.out.printf("Elements before Linear" +
                    " Search Move To Front: ");
 
  // Function Call for
  // displaying the array
  // arr[]
  Display(arr);
 
  // Function Call for Move
  // to front operation
  LinearSearchMoveToFront(arr, 14);
 
  System.out.printf("Elements after Linear" +
                    " Search Move To Front: ");
 
  // Function Call for displaying
  // the array arr[]
  Display(arr);
}
}
 
// This code is contributed by gauravrajput1

C＃

// C# program to implement
// the move to front to optimized
// Linear Search
using System;
class GFG{
 
// Structure of the array
public class Array
{
  public int []A = new int[10];
  public int size;
  public int length;
  public Array(int []A,
               int size,
               int length)
  {
    this.A = A;
    this.size = size;
    this.length = length;
  }
};
 
// Function to print the
// array element
static void Display(Array arr)
{
  int i;
 
  // Traverse the array []arr
  for (i = 0;
       i < arr.length; i++)
  {
    Console.Write(" " + arr.A[i]);
  }
  Console.Write("\n");
}
 
// Function that performs the
// move to front operation for
// Linear Search
static int LinearSearchMoveToFront(Array arr,
                                   int key)
{
  int i;
 
  // Traverse the array
  for (i = 0; i < arr.length; i++)
  {
    // If key is found, then swap
    // the element with 0-th index
    if (key == arr.A[i])
    {
      int temp = arr.A[i];
      arr.A[i] = arr.A[0];
      arr.A[0] = temp;
      return i;
    }
  }
  return -1;
}
 
// Driver code
public static void Main(String[] args)
{
  // Given array []arr
  int []a = {2, 23, 14, 5,
             6, 9, 8, 12 };
   
  Array arr = new Array(a, 10, 8);
  Console.Write("Elements before Linear" +
                " Search Move To Front: ");
 
  // Function Call for
  // displaying the array
  // []arr
  Display(arr);
 
  // Function Call for Move
  // to front operation
  LinearSearchMoveToFront(arr, 14);
 
  Console.Write("Elements after Linear" +
                " Search Move To Front: ");
 
  // Function Call for displaying
  // the array []arr
  Display(arr);
}
}
 
// This code is contributed by gauravrajput1

输出：
线性搜索前的元素移到前面：2 23 14 5 6 9 8 12
线性搜索后的元素移到前面：14 23 2 5 6 9 8 12

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