Reallocation of elements based on Locality of Reference

Consider a problem where same elements are likely to be searched again and again. Implement search operation efficiently.

Examples :

Input : arr[] = {12 25 36 85 98 75 89 15 63 66
                               64 74 27 83 97}
          q[] = {63, 63, 86, 63, 78}
Output : Yes Yes No Yes No
We need one by one search items of q[] in arr[].
The element 63 is present, 78 and 86 are not present.

The idea is simple, we move the searched element to front of the array so that it can be searched quickly next time.

C++

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// C++ program to implement search for an item
// that is searched again and again.
#include <bits/stdc++.h>
using namespace std;
  
// A function to perform sequential search.
bool search(int arr[], int n, int x)
{
    // Linearly search the element
    int res = -1;
    for (int i = 0; i < n; i++) 
        if (x == arr[i])
        res = i; 
  
    // If not found
    if (res == -1)
        return false
  
    // Shift elements before one position
    int temp = arr[res];
    for (int i = res; i > 0; i--)
        arr[i] = arr[i - 1];
  
    arr[0] = temp;
    return true;
}
  
// Driver Code
int main()
{
    int arr[] = { 12, 25, 36, 85, 98, 75, 89, 15,
                    63, 66, 64, 74, 27, 83, 97 };
    int q[] = {63, 63, 86, 63, 78};
    int n = sizeof(arr)/sizeof(arr[0]);
    int m = sizeof(q)/sizeof(q[0]);
    for (int i=0; i<m; i++)
    search(arr, n, q[i])? cout << "Yes "
                        : cout << "No ";     
  
    return 0;
}

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Java

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// Java program to implement search for an item
// that is searched again and again.
import java.util.*;
  
class solution
{
  
// A function to perform sequential search.
static boolean search(int[] arr, int n, int x)
{
    // Linearly search the element
    int res = -1;
    for (int i = 0; i < n; i++) 
        if (x == arr[i])
        res = i; 
  
    // If not found
    if (res == -1)
        return false
  
    // Shift elements before one position
    int temp = arr[res];
    for (int i = res; i > 0; i--)
        arr[i] = arr[i - 1];
  
    arr[0] = temp;
    return true;
}
  
// Driver Code
public static void main(String args[])
{
    int []arr = { 12, 25, 36, 85, 98, 75, 89, 15,
                    63, 66, 64, 74, 27, 83, 97 };
    int []q = {63, 63, 86, 63, 78};
    int n = arr.length;
    int m = q.length;
    for (int i=0; i<m; i++)
    {
    if(search(arr, n, q[i]) == true)
        System.out.print("Yes ");
    else
        System.out.print("No ");
    }
}
}
// This code is contributed by
// Shashank_Sharma

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Python3

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# Python 3 program to implement search for 
# an item that is searched again and again.
  
# A function to perform sequential search.
def search(arr, n, x):
      
    # Linearly search the element
    res = -1
    for i in range(0, n, 1):
        if (x == arr[i]):
            res =
  
    # If not found
    if (res == -1):
        return False
  
    # Shift elements before 
    # one position
    temp = arr[res]
    i = res
    while(i > 0):
        arr[i] = arr[i - 1]
        i -= 1
  
    arr[0] = temp
    return True
  
# Driver Code
if __name__ == '__main__':
    arr = [12, 25, 36, 85, 98, 75, 89
           15, 63, 66, 64, 74, 27, 83, 97]
    q = [63, 63, 86, 63, 78]
    n = len(arr)
    m = len(q)
    for i in range(0, m, 1):
        if(search(arr, n, q[i])):
            print("Yes", end = " ")
        else:
            print("No", end = " ")
  
# This code is contributed by
# Surendra_Gangwar

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C#

// C# program to implement search for an
// item that is searched again and again.
using System;

class GFG
{

// A function to perform sequential search.
static bool search(int[] arr, int n, int x)
{
// Linearly search the element
int res = -1;
for (int i = 0; i < n; i++) if (x == arr[i]) res = i; // If not found if (res == -1) return false; // Shift elements before one position int temp = arr[res]; for (int i = res; i > 0; i–)
arr[i] = arr[i – 1];

arr[0] = temp;
return true;
}

// Driver Code
public static void Main()
{
int[] arr = { 12, 25, 36, 85, 98, 75, 89, 15,
63, 66, 64, 74, 27, 83, 97 };
int[] q = {63, 63, 86, 63, 78};
int n = arr.Length;
int m = q.Length;
for (int i = 0; i < m; i++) { if(search(arr, n, q[i]) == true) Console.Write("Yes "); else Console.Write("No "); } } } // This code is contributed by // Akanksha Rai [tabby title="PHP"]

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<?php
// PHP program to implement search for an
// item that is searched again and again.
  
// A function to perform sequential search.
function search($arr, $n, $x)
{
    // Linearly search the element
    $res = -1;
    for ($i = 0; $i < $n; $i++) 
        if ($x == $arr[$i])
        $res = $i
  
    // If not found
    if ($res == -1)
        return false; 
  
    // Shift elements before one position
    $temp = $arr[$res];
    for ($i = $res; $i > 0; $i--)
        $arr[$i] = $arr[$i - 1];
  
    $arr[0] = $temp;
    return true;
}
  
// Driver Code
$arr = array(12, 25, 36, 85, 98, 75, 89, 15,
                 63, 66, 64, 74, 27, 83, 97);
$q = array(63, 63, 86, 63, 78);
$n = sizeof($arr);
$m = sizeof($q);
  
for ($i = 0; $i < $m; $i++)
    if(search($arr, $n, $q[$i]))
        echo "Yes ";
    else
        echo "No ";     
  
// This code is contributed
// by Akanksha Rai

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Output:

Yes Yes No Yes No 

Further Thoughts : We can do better by using a linked list. In linked list, moving an item to front can be done in O(1) time.
The best solution would be to use Splay Tree (a data structure designed for this purpose). Splay tree supports insert, search and delete operations in O(Log n) time on average. Also, splay tree is a BST, so we can quickly print elements in sorted order.



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