Data Structures - Linked List Other Related Topics
Data Structures - Linked List Other Related Topics

Linked List - Search an element

Searching an element in a linked list requires creating a temp node pointing to the head of the linked list. Along with this, two more variables are required to track search and track index of the current node. If the temp node is not null at the start, then traverse the linked list to check if current node value matches with the search value. If it matches then update search tracker variable and stop traversing the list, else keep on traversing the list. If the temp node is empty at the start, then the list contains no item.

The function SearchElement is created for this purpose. It is a 4-step process.

void SearchElement(int searchValue) {
  
  //1. create a temp node pointing to head
  Node* temp = head;
  
  //2. create two variables: found - to track
  //   search, idx - to track current index
  int found = 0;
  int i = 0;

  //3. if the temp node is not null check the
  //   node value with searchValue, if found 
  //   update variables and break the loop, else
  //   continue searching till temp node is not null 
  if(temp != NULL) {
    while(temp != NULL) {
      i++;
      if(temp->data == searchValue) {
        found++;
        break;
      }
      temp = temp->next;
    }
    if (found == 1) {
      cout<<searchValue<<" is found at index = "<<i<<".\n";
    } else {
      cout<<searchValue<<" is not found in the list.\n";
    }
  } else {
    
    //4. If the temp node is null at the start, 
    //   the list is empty
    cout<<"The list is empty.\n";
  }
} 

void SearchElement(struct Node* head_ref, int searchValue) {
  
  //1. create a temp node pointing to head
  struct Node* temp = head_ref;
  
  //2. create two variables: found - to track
  //   search, idx - to track current index
  int found = 0;
  int i = 0;

  //3. if the temp node is not null check the
  //   node value with searchValue, if found 
  //   update variables and break the loop, else
  //   continue searching till temp node is not null  
  if(temp != NULL) {
    while(temp != NULL) {
      i++;
      if(temp->data == searchValue) {
        found++;
        break;
      }
      temp = temp->next;
    }
    if (found == 1) {
      printf("%i is found at index = %i.\n", searchValue, i);
    } else {
      printf("%i is not found in the list.\n", searchValue);
    }
  } else {
    
    //4. If the temp node is null at the start, 
    //   the list is empty
    printf("The list is empty.\n");
  }
} 

def SearchElement(self, searchValue):
  
  #1. create a temp node pointing to head
  temp = self.head
  
  #2. create two variables: found - to track
  #   search, idx - to track current index
  found = 0
  i = 0 

  #3. if the temp node is not null check the
  #   node value with searchValue, if found 
  #   update variables and break the loop, else
  #   continue searching till temp node is not null 
  if(temp != None):
    while (temp != None):
      i += 1
      if(temp.data == searchValue):
        found += 1
        break
      temp = temp.next
    if(found == 1):
      print(searchValue,"is found at index =", i)
    else:
      print(searchValue,"is not found in the list.")
  else:
    
    #4. If the temp node is null at the start, 
    #   the list is empty
    print("The list is empty.")

void SearchElement(int searchValue) {
  
  //1. create a temp node pointing to head
  Node temp = new Node();
  temp = this.head;

  //2. create two variables: found - to track
  //   search, idx - to track current index
  int found = 0;
  int i = 0;

  //3. if the temp node is not null check the
  //   node value with searchValue, if found 
  //   update variables and break the loop, else
  //   continue searching till temp node is not null  
  if(temp != null) {
    while(temp != null) {
      i++;
      if(temp.data == searchValue) {
        found++;
        break;
      }
      temp = temp.next;
    }
    if (found == 1) {
      System.out.println(searchValue + " is found at index = " + i +".");
    } else {
      System.out.println(searchValue + " is not found in the list.");
    }
  } else {
    
    //4. If the temp node is null at the start, 
    //   the list is empty
    System.out.println("The list is empty.");
  }
}   

public void SearchElement(int searchValue) {
  
  //1. create a temp node pointing to head
  Node temp = new Node();
  temp = this.head;

  //2. create two variables: found - to track
  //   search, idx - to track current index
  int found = 0;
  int i = 0;

  //3. if the temp node is not null check the
  //   node value with searchValue, if found 
  //   update variables and break the loop, else
  //   continue searching till temp node is not null  
  if(temp != null) {
    while(temp != null) {
      i++;
      if(temp.data == searchValue) {
        found++;
        break;
      }
      temp = temp.next;
    }
    if (found == 1) {
      Console.WriteLine(searchValue + " is found at index = " + i +".");
    } else {
      Console.WriteLine(searchValue + " is not found in the list.");
    }
  } else {
    
    //4. If the temp node is null at the start, 
    //   the list is empty
    Console.WriteLine("The list is empty.");
  }
}  

public function SearchElement($searchValue) {
  
  //1. create a temp node pointing to head
  $temp = new Node();
  $temp = $this->head;

  //2. create two variables: found - to track
  //   search, idx - to track current index
  $found = 0;
  $i = 0;

  //3. if the temp node is not null check the
  //   node value with searchValue, if found 
  //   update variables and break the loop, else
  //   continue searching till temp node is not null  
  if($temp != null) {
    while($temp != null) {
      $i++;
      if($temp->data == $searchValue) {
        $found++;
        break;
      }
      $temp = $temp->next;
    }
    if ($found == 1) {
      echo $searchValue." is found at index = ".$i.".\n";
    } else {
      echo $searchValue." is not found in the list.\n";
    }
  } else {
    
    //4. If the temp node is null at the start, 
    //   the list is empty
    echo "The list is empty.\n";
  }
}

The below is a complete program that uses above discussed concept to search an element in a given linked list.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }

    //Add new element at the end of the list
    void push_back(int newElement) {
      Node* newNode = new Node();
      newNode->data = newElement;
      newNode->next = NULL; 
      if(head == NULL) {
        head = newNode;
      } else {
        Node* temp = head;
        while(temp->next != NULL)
          temp = temp->next;
        temp->next = newNode;
      }    
    }

    //Search an element in the list
    void SearchElement(int searchValue) {   
      Node* temp = head;
      int found = 0;
      int i = 0;

      if(temp != NULL) {
        while(temp != NULL) {
          i++;
          if(temp->data == searchValue) {
            found++;
            break;
          }
          temp = temp->next;
        }
        if (found == 1) {
          cout<<searchValue<<" is found at index = "<<i<<".\n";
        } else {
          cout<<searchValue<<" is not found in the list.\n";
        }
      } else {
        cout<<"The list is empty.\n";
      }
    } 

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"The list contains: ";
        while(temp != NULL) {
          cout<<temp->data<<" ";
          temp = temp->next;
        }
        cout<<"\n";
      } else {
        cout<<"The list is empty.\n";
      }
    }   
};

// test the code 
int main() {
  LinkedList MyList;

  //Add three elements at the end of the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);

  //traverse to display the content of the list.
  MyList.PrintList();

  //search for element in the list
  MyList.SearchElement(10);
  MyList.SearchElement(15);
  MyList.SearchElement(20);

  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.

#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
  int data;
  struct Node* next;
};

//Add new element at the end of the list
void push_back(struct Node** head_ref, int newElement) {  
  struct Node *newNode, *temp;
  newNode = (struct Node*)malloc(sizeof(struct Node)); 
  newNode->data = newElement;  
  newNode->next = NULL;
  if(*head_ref == NULL) {
    *head_ref = newNode; 
  } else {
    temp = *head_ref;
    while(temp->next != NULL) {
      temp = temp->next;
    }    
    temp->next = newNode;
  }
}

//Search an element in the list
void SearchElement(struct Node* head_ref, int searchValue) {
  struct Node* temp = head_ref;
  int found = 0;
  int i = 0;

  if(temp != NULL) {
    while(temp != NULL) {
      i++;
      if(temp->data == searchValue) {
        found++;
        break;
      }
      temp = temp->next;
    }
    if (found == 1) {
      printf("%i is found at index = %i.\n", searchValue, i);
    } else {
      printf("%i is not found in the list.\n", searchValue);
    }
  } else {
    printf("The list is empty.\n");
  }
} 

//display the content of the list
void PrintList(struct Node* head_ref) {
  struct Node* temp = head_ref;
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (temp != NULL) {
      printf("%i ",temp->data);
      temp = temp->next;  
    }
    printf("\n");
  } else {
    printf("The list is empty.\n");
  }   
}

// test the code 
int main() {
  struct Node* MyList = NULL;

  //Add three elements at the end of the list.
  push_back(&MyList, 10);
  push_back(&MyList, 20);
  push_back(&MyList, 30);

  //traverse to display the content of the list.
  PrintList(MyList);

  //search for element in the list
  SearchElement(MyList, 10);
  SearchElement(MyList, 15);
  SearchElement(MyList, 20);

  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None

#class Linked List
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the end of the list
  def push_back(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      return
    else:
      temp = self.head
      while(temp.next != None):
        temp = temp.next
      temp.next = newNode

  #Search an element
  def SearchElement(self, searchValue):
    temp = self.head
    found = 0
    i = 0 

    if(temp != None):
      while (temp != None):
        i += 1
        if(temp.data == searchValue):
          found += 1
          break
        temp = temp.next
      if(found == 1):
        print(searchValue,"is found at index =", i)
      else:
        print(searchValue,"is not found in the list.")
    else:
      print("The list is empty.")

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (temp != None):
        print(temp.data, end=" ")
        temp = temp.next
      print()
    else:
      print("The list is empty.")

# test the code                 
MyList = LinkedList()

#Add three elements at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)

#traverse to display the content of the list.
MyList.PrintList()

#search for element in the list
MyList.SearchElement(10)
MyList.SearchElement(15)
MyList.SearchElement(20)

The above code will give the following output: 

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.

//node structure
class Node {
    int data;
    Node next;
};

class LinkedList {
  Node head;

  LinkedList(){
    head = null;
  }

  //Add new element at the end of the list
  void push_back(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null; 
    if(head == null) {
      head = newNode;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
    }    
  }

  //Search an element in the list
  void SearchElement(int searchValue) {
    Node temp = new Node();
    temp = this.head;

    int found = 0;
    int i = 0;

    if(temp != null) {
      while(temp != null) {
        i++;
        if(temp.data == searchValue) {
          found++;
          break;
        }
        temp = temp.next;
      }
      if (found == 1) {
        System.out.println(searchValue + " is found at index = " + i +".");
      } else {
        System.out.println(searchValue + " is not found in the list.");
      }
    } else {
      System.out.println("The list is empty.");
    }
  }   

  //display the content of the list
  void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      System.out.print("The list contains: ");
      while(temp != null) {
        System.out.print(temp.data + " ");
        temp = temp.next;
      }
      System.out.println();
    } else {
      System.out.println("The list is empty.");
    }
  }    
};

// test the code
public class Implementation {
  public static void main(String[] args) {
    LinkedList MyList = new LinkedList();

    //Add three elements at the end of the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);

    //traverse to display the content of the list.
    MyList.PrintList(); 

    //search for element in the list
    MyList.SearchElement(10);
    MyList.SearchElement(15);
    MyList.SearchElement(20);
  }
}

The above code will give the following output: 

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.

using System;

//node structure
class Node {
  public int data;
  public Node next;
};

class LinkedList {
  Node head;

  public LinkedList(){
    head = null;
  }
  
  //Add new element at the end of the list
  public void push_back(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null; 
    if(head == null) {
      head = newNode;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
    }    
  }

  //Search an element in the list
  public void SearchElement(int searchValue) {
    Node temp = new Node();
    temp = this.head;
    int found = 0;
    int i = 0;

    if(temp != null) {
      while(temp != null) {
        i++;
        if(temp.data == searchValue) {
          found++;
          break;
        }
        temp = temp.next;
      }
      if (found == 1) {
        Console.WriteLine(searchValue + " is found at index = " + i +".");
      } else {
        Console.WriteLine(searchValue + " is not found in the list.");
      }
    } else {
      Console.WriteLine("The list is empty.");
    }
  }  

  //display the content of the list
  public void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      Console.Write("The list contains: ");
      while(temp != null) {
        Console.Write(temp.data + " ");
        temp = temp.next;
      }
      Console.WriteLine();
    } else {
      Console.WriteLine("The list is empty.");
    }
  }     
};

// test the code
class Implementation {
  static void Main(string[] args) {
    LinkedList MyList = new LinkedList();

    //Add three elements at the end of the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);

    //traverse to display the content of the list.
    MyList.PrintList();   

    //search for element in the list
    MyList.SearchElement(10);
    MyList.SearchElement(15);
    MyList.SearchElement(20);
  }
}

The above code will give the following output: 

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.

<?php
//node structure
class Node {
  public $data;
  public $next;
}

class LinkedList {
  public $head;

  public function __construct(){
    $this->head = null;
  }
  
  //Add new element at the end of the list
  public function push_back($newElement) {
    $newNode = new Node();
    $newNode->data = $newElement;
    $newNode->next = null; 
    if($this->head == null) {
      $this->head = $newNode;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next != null) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
    }    
  }

  //Search an element in the list
  public function SearchElement($searchValue) {
    $temp = new Node();
    $temp = $this->head;
    $found = 0;
    $i = 0;

    if($temp != null) {
      while($temp != null) {
        $i++;
        if($temp->data == $searchValue) {
          $found++;
          break;
        }
        $temp = $temp->next;
      }
      if ($found == 1) {
        echo $searchValue." is found at index = ".$i.".\n";
      } else {
        echo $searchValue." is not found in the list.\n";
      }
    } else {
      echo "The list is empty.\n";
    }
  }  

  //display the content of the list
  public function PrintList() {
    $temp = new Node();
    $temp = $this->head;
    if($temp != null) {
      echo "The list contains: ";
      while($temp != null) {
        echo $temp->data." ";
        $temp = $temp->next;
      }
      echo "\n";
    } else {
      echo "The list is empty.\n";
    }
  }   
};

// test the code 
$MyList = new LinkedList();

//Add three elements at the end of the list.
$MyList->push_back(10);
$MyList->push_back(20);
$MyList->push_back(30);

//traverse to display the content of the list.
$MyList->PrintList();

//search for element in the list
$MyList->SearchElement(10);
$MyList->SearchElement(15);
$MyList->SearchElement(20);
?>

The above code will give the following output: 

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.
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