JavaScript program adds two numbers represented by a linked list - Setup 1

Adding two numbers is a simple task, but it can be tricky if the numbers are given in the form of a linked list. Each node of the linked list contains the number of the number it represents in a continuous manner from the first node to the last node. We will get two linked lists representing two different numbers and we have to add them and return the third number in the form of a linked list.

enter

1 -> 2 -> 3 -> null
3 -> 2 -> 4 -> null

Output

4 -> 4 -> 7 -> null

Description: Given that the first number is 123, the second number is 324, and their sum is 447, we return it in the form of a linked list.

Convert to number method

In this method, first, we convert the given number from linked list representation to integer form and then apply addition operation. After that, we convert the result into a linked list and finally return to print the data present in the answer linked list.

Example

// class to create the structure of the nodes 
class Node{
   constructor(data){
      this.value = data;
      this.next = null;
   }
}

// function to print the linked list
function print(head){
   var temp = head;
   var ans = ""
   while(temp.next != null){
      ans += temp.value;
      ans += " -> "
      temp = temp.next
   }
   ans += temp.value
   ans += " -> null"
    
   console.log(ans)
}

// function to add data in linked list 
function add(data, head, tail){
   return tail.next = new Node(data);
}

// function to convert linked list to number 
function LL_to_int(head){
   var temp = "";
   var cur = head;
   while(cur != null){
      temp += cur.value.toString();
      cur = cur.next;
   }
   return parseInt(temp);
}

// function to convert number to linked list
function num_to_LL(num){
   var str = num.toString();
   var head = new Node(str[0]-'0');
   var tail = head;
   for(var i = 1; i<str.length; i++){
      tail = add(str[i]-'0',head, tail);
   }
   
   // final number is 
   console.log("The final answer is: ")
   print(head);
}

// defining first number
var num1  = new Node(1)
var tail  = num1
tail = add(2,num1, tail)
tail = add(3,num1, tail)
console.log("The given first number is: ")
print(num1)

// defining second number
var num2 = new Node(3)
tail  = num2
tail = add(2,num2, tail)
tail = add(4,num2, tail)
console.log("The given second number is: ")
print(num2)

// converting both the linked list into the actual values
int_num1 = LL_to_int(num1)
int_num2 = LL_to_int(num2)
var ans = int_num1 + int_num2;

// converting number to the linked list 
num_to_LL(ans);

Output

The given first number is: 
1 -> 2 -> 3 -> null
The given second number is: 
3 -> 2 -> 4 -> null
The final answer is: 
4 -> 4 -> 7 -> null

Time and space complexity

The time complexity of the above code is (M N), where M and N are the sizes of the given linked list.

The space complexity of the above code is O(N) because we create a new linked list.

Another method

In this method, we will add linked list elements by traversing from the end to the first node until the first linked list value becomes zero. When once becomes zero, set its value to zero and move until they both become zero.

Example

// class to create the structure of the nodes 
class Node{
   constructor(data){
      this.value = data;
      this.next = null;
   }
}

// function to print the linked list
function print(head){
   var temp = head;
   var ans = ""
   while(temp.next != null){
      ans += temp.value;
      ans += " -> "
      temp = temp.next
   }
   ans += temp.value
   ans += " -> null"
   console.log(ans)
}

// function to add data in linked list 
function add(data, head, tail){
   return tail.next = new Node(data);
}

// function to convert string to linked list
function num_to_LL(str){
   var head = new Node(str[str.length-1]-'0');
   var tail = head;
   for(var i = str.length-2; i>=0; i--){
      tail = add(str[i]-'0',head, tail);
   }
   
   // final number is 
   console.log("The final answer is: ")
   print(head);
}

// function to add values of the linked lists
function addLL(ll1, ll2){
   var str = "";
   var carry = 0;
   while((ll1 != null) || (ll2 != null)){
      if(ll1 == null){
         carry += ll2.value;
         ll2 = ll2.next;
      }  else if(ll2 == null){
         carry += ll1.value;
         ll1 = ll1.next;
      }  else {
         carry += ll1.value + ll2.value;
         ll2 = ll2.next;
         ll1 = ll1.next;
      }
      str += (carry%10).toString();
      carry /= 10;
      carry = Math.floor(carry);
   }
   if(carry != 0){
      str += (carry%10).toString();
   }
   
   // calling function to print the answer
   num_to_LL(str);
}

// defining first number in reverse manner 
var num1  = new Node(3)
var tail  = num1
tail = add(2,num1, tail)
tail = add(1,num1, tail)
console.log("The given first number in reverse manner is: ")
print(num1)

// defining second number
var num2 = new Node(4)
tail  = num2
tail = add(2,num2, tail)
tail = add(3,num2, tail)
console.log("The given second number in reverse manner is: ")
print(num2)

// calling to the add function 
addLL(num1,num2);

Output

The given first number is: 
1 -> 2 -> 3 -> null
The given second number is: 
3 -> 2 -> 4 -> null
The final answer is: 
4 -> 4 -> 7 -> null

in conclusion

In this tutorial, we implemented JavaScript code to add two numbers given in the form of a linked list and return the result in the form of a linked list. We implemented two methods with O(N) time and space complexity.

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