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Maximum occurring character in a linked list
  • Difficulty Level : Easy
  • Last Updated : 31 Dec, 2020

Given a linked list of characters. The task is to find the maximum occurring character in the linked list. if there are multiple answers, return the first maximum occurring character.

Examples: 

Input  : g -> e -> e -> k -> s
Output : e

Input  : a -> a -> b -> b -> c -> c -> d -> d
Output : d

Method 1: 
Iteratively count the frequency of each character in a string and return the one which has maximum occurrence.

C++




// C++ program to count the maximum
// occurring character in linked list
#include <bits/stdc++.h>
using namespace std;
 
/* Link list node */
struct Node {
  char data;
  struct Node *next;
};
 
char maxChar(struct Node *head) {
  struct Node *p = head;
 
  int max = -1;
  char res;
 
  while (p != NULL) {
 
    // counting the frequency of current element
    // p->data
    struct Node *q = p->next;
    int count = 1;
    while (q != NULL) {
      if (p->data == q->data)
        count++;
 
      q = q->next;
    }
 
    // if current counting is greater than max
    if (max < count) {
      res = p->data;
      max = count;
    }
 
    p = p->next;
  }
 
  return res;
}
 
/* Push a node to linked list. Note that
   this function changes the head */
void push(struct Node **head_ref, char new_data) {
  struct Node *new_node = new Node;
  new_node->data = new_data;
  new_node->next = (*head_ref);
  (*head_ref) = new_node;
}
 
/* Driver program to test above function*/
int main() {
  /* Start with the empty list */
  struct Node *head = NULL;
  char str[] = "skeegforskeeg";
  int i;
 
  // this will create a linked list of
  // character "geeksforgeeks"
  for (i = 0; str[i] != '\0'; i++)
    push(&head, str[i]);
 
  cout << maxChar(head);
 
  return 0;
}

Java




// Java program to count the
// maximum occurring character
// in linked list
import java.util.*;
class GFG{
 
// Link list node
static class Node
{
  char data;
  Node next;
};
   
static Node head_ref;
   
static char maxChar(Node head)
{
  Node p = head;
  int max = -1;
  char res = '0';
 
  while (p != null)
  {
    // counting the frequency
    // of current element
    // p.data
    Node q = p.next;
    int count = 1;
     
    while (q != null)
    {
      if (p.data == q.data)
        count++;
 
      q = q.next;
    }
 
    // if current counting
    // is greater than max
    if (max < count)
    {
      res = p.data;
      max = count;
    }
 
    p = p.next;
  }
 
  return res;
}
 
// Push a node to linked list.
// Note that this function
// changes the head
static void push(char new_data)
{
  Node new_node = new Node();
  new_node.data = new_data;
  new_node.next = head_ref;
  head_ref = new_node;
}
 
// Driver code
public static void main(String[] args)
{
  // Start with the empty list
   head_ref = null;
  String str = "skeegforskeeg";
  char st[] = str.toCharArray();
  int i;
 
  // this will create a linked
  // list of character "geeksforgeeks"
  for (i = 0; i < st.length; i++)
     push(st[i]);
 
  System.out.print(maxChar(head_ref));
}
}
 
// This code is contributed by shikhasingrajput

C#




// C# program to count the
// maximum occurring character
// in linked list
using System;
class GFG
{
  
// Link list node
class Node
{
  public char data;
  public Node next;
};
    
static Node head_ref;
    
static char maxChar(Node head)
{
  Node p = head;
  int max = -1;
  char res = '0';
  
  while (p != null)
  {
     
    // counting the frequency
    // of current element
    // p.data
    Node q = p.next;
    int count = 1;
      
    while (q != null)
    {
      if (p.data == q.data)
        count++;
      q = q.next;
    }
  
    // if current counting
    // is greater than max
    if (max < count)
    {
      res = p.data;
      max = count;
    }
  
    p = p.next;
  }
  
  return res;
}
  
// Push a node to linked list.
// Note that this function
// changes the head
static void push(char new_data)
{
  Node new_node = new Node();
  new_node.data = new_data;
  new_node.next = head_ref;
  head_ref = new_node;
}
  
// Driver code
public static void Main(string[] args)
{
   
  // Start with the empty list
   head_ref = null;
  string str = "skeegforskeeg";
  char []st = str.ToCharArray();
  int i;
  
  // this will create a linked
  // list of character "geeksforgeeks"
  for (i = 0; i < st.Length; i++)
     push(st[i]);
  
  Console.Write(maxChar(head_ref));
}
}
 
// This code is contributed by rutvik_56
Output: 
e

 

Time complexity: (N*N)



Method 2: (use count array) 
Create a count array and count each character frequency return the maximum occurring character. 

C++




// C++ program to count the maximum
// occurring character in linked list
#include <bits/stdc++.h>
using namespace std;
 
/* Link list node */
struct Node {
  char data;
  struct Node *next;
};
 
char maxChar(struct Node *head) {
  struct Node *p = head;
  int hash[256] = {0};
 
  // Storing element's frequencies
  // in a hash table.
  while (p != NULL) {
    hash[p->data]++;
    p = p->next;
  }
 
  p = head;
 
  int max = -1;
  char res;
 
  // calculating the first maximum element
  while (p != NULL) {
    if (max < hash[p->data]) {
      res = p->data;
      max = hash[p->data];
    }
    p = p->next;
  }
  return res;
}
 
/* Push a node to linked list. Note that
   this function changes the head */
void push(struct Node **head_ref, char new_data) {
  struct Node *new_node = new Node;
  new_node->data = new_data;
  new_node->next = (*head_ref);
  (*head_ref) = new_node;
}
 
/* Driver program to test above function*/
int main() {
  struct Node *head = NULL;
  char str[] = "skeegforskeeg";
  for (int i = 0; str[i] != '\0'; i++)
    push(&head, str[i]);
  cout << maxChar(head);
  return 0;
}

Java




// Java program to count the maximum
// occurring character in linked list
import java.util.*;
 
class GFG
{
 
/* Link list node */
static class Node
{
    char data;
    Node next;
};
 
static Node head;
static char maxChar(Node head)
{
    Node p = head;
    int []hash = new int[256];
     
    // Storing element's frequencies
    // in a hash table.
    while (p != null)
    {
        hash[p.data]++;
        p = p.next;
    }
     
    p = head;
     
    int max = -1;
    char res = 0;
     
    // calculating the first maximum element
    while (p != null)
    {
        if (max < hash[p.data])
        {
            res = p.data;
            max = hash[p.data];
        }
        p = p.next;
    }
    return res;
}
     
/* Push a node to linked list. Note that
this function changes the head */
static void push(Node head_ref, char new_data)
{
    Node new_node = new Node();
    new_node.data = new_data;
    new_node.next = head_ref;
    head_ref = new_node;
    head = head_ref;
}
 
// Driver Code
public static void main(String[] args)
{
    head = null;
    char str[] = "skeegforskeeg".toCharArray();
    for (int i = 0; i < str.length; i++)
    {
        push(head, str[i]);
    }
    System.out.println(maxChar(head));
    }
}
 
// This code is contributed by Rajput-Ji

Python3




# Python3 program to count the maximum
# occurring character in linked list
  
# Link list node
class Node:
     
    def __init__(self):
         
        self.data = ''
        self.next = None
 
def maxChar(head):
     
    p = head
    hash = [0 for i in range(256)]
 
    # Storing element's frequencies
    # in a hash table.
    while (p != None):
      hash[ord(p.data)] += 1
      p = p.next
 
    p = head
 
    max = -1
    res = ''
 
    # Calculating the first maximum element
    while (p != None):
      if (max < hash[ord(p.data)]):
        res = p.data
        max = hash[ord(p.data)]
       
      p = p.next
     
    return res
 
# Push a node to linked list. Note that
# this function changes the head
def push(head_ref, new_data):
     
    new_node = Node()
    new_node.data = new_data
    new_node.next = (head_ref)
    (head_ref) = new_node
    return head_ref
 
# Driver Code
if __name__=='__main__':
     
    head = None
    str = "skeegforskeeg"
     
    for i in range(len(str)):
        head  = push(head, str[i])
         
    print(maxChar(head))
   
# This code is contributed by pratham76

C#




// C# program to count the maximum
// occurring character in linked list
using System;
     
public class GFG
{
  
/* Link list node */
class Node
{
    public char data;
    public Node next;
};
  
static Node head;
static char maxChar(Node head)
{
    Node p = head;
    int []hash = new int[256];
      
    // Storing element's frequencies
    // in a hash table.
    while (p != null)
    {
        hash[p.data]++;
        p = p.next;
    }
      
    p = head;
      
    int max = -1;
    char res= '\x0000';
      
    // calculating the first maximum element
    while (p != null)
    {
        if (max < hash[p.data])
        {
            res = p.data;
            max = hash[p.data];
        }
        p = p.next;
    }
    return res;
}
      
/* Push a node to linked list. Note that
this function changes the head */
static void push(Node head_ref, char new_data)
{
    Node new_node = new Node();
    new_node.data = new_data;
    new_node.next = head_ref;
    head_ref = new_node;
    head = head_ref;
}
  
// Driver Code
public static void Main(String[] args)
{
    head = null;
    char []str = "skeegforskeeg".ToCharArray();
    for (int i = 0; i < str.Length; i++)
    {
        push(head, str[i]);
    }
    Console.WriteLine(maxChar(head));
    }
}
 
// This code is contributed by 29AjayKumar
Output: 
e

 

Time complexity: (N)

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