Subtract 1 from a number represented as Linked List
Last Updated :
23 Jul, 2025
Given the head of the linked list representing a positive integer, the task is to print the updated linked list after subtracting 1 from it.
Examples:
Input: LL = 1 -> 2 -> 3 -> 4
Output: 1 -> 2 -> 3 -> 3
Input: LL = 1 -> 2
Output: 1 -> 1
Approach: The given problem can be solved by using recursion. Follow the steps below to solve the problem:
- Define a function, say subtractOneUtil(Node *head) that takes the head of the linked list as the arguments and perform the following steps:
- Base Case: If the head node of the Linked List is NULL, then return -1 from that recursive call.
- Recursive Call: Recursively call for the next node of the linked list and let the value returned by this recursive call be borrow.
- If the value of borrow is -1 and the value of the head node is 0, then update the value of the head node to 9 and return -1 from the current recursive call.
- Otherwise, decrement the value of the head node by 1 and return 0 from the current recursive call.
- Subtract 1 from the Linked List by calling the above function as subtractOneUtil(head).
- If the update linked list has leading 0s, then move the head pointer.
- After completing the above steps, print the updated linked list as the resultant linked list.
Below is the implementation of the above approach:
C++
// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
// Linked list Node
class Node {
public:
int data;
Node* next;
};
// Function to create a new node with
// the given data
Node* newNode(int data)
{
// Create a new node
Node* new_node = new Node;
new_node->data = data;
new_node->next = NULL;
// Return the created node
return new_node;
}
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
int subtractOneUtil(Node* head)
{
// Base Case
if (head == NULL)
return -1;
// Recursively call for the next
// node of the head
int borrow = subtractOneUtil(
head->next);
// If there is a borrow
if (borrow == -1) {
// If the head data is 0, then
// update it with 9 and return -1
if (head->data == 0) {
head->data = 9;
return -1;
}
// Otherwise, decrement head's
// data by 1 and return 0
else {
head->data = head->data - 1;
return 0;
}
}
// Otherwise, return 0
else {
return 0;
}
}
// Function to subtract 1 from the given
// Linked List representation of number
Node* subtractOne(Node* head)
{
// Recursively subtract 1 from
// the Linked List
subtractOneUtil(head);
// Increment the head pointer
// if there are any leading zeros
while (head and head->next
and head->data == 0) {
head = head->next;
}
return head;
}
// Function to print a linked list
void printList(Node* node)
{
// Iterate until node is NULL
while (node != NULL) {
cout << node->data;
node = node->next;
}
cout << endl;
}
// Driver Code
int main()
{
Node* head = newNode(1);
head->next = newNode(0);
head->next->next = newNode(0);
head->next->next->next = newNode(0);
cout << "List is ";
printList(head);
head = subtractOne(head);
cout << "Resultant list is ";
printList(head);
return 0;
}
// Java program for the above approach
import java.util.*;
class GFG{
// Linked list Node
static class Node
{
int data;
Node next;
};
// Function to create a new node with
// the given data
static Node newNode(int data)
{
// Create a new node
Node new_node = new Node();
new_node.data = data;
new_node.next = null;
// Return the created node
return new_node;
}
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
static int subtractOneUtil(Node head)
{
// Base Case
if (head == null)
return -1;
// Recursively call for the next
// node of the head
int borrow = subtractOneUtil(
head.next);
// If there is a borrow
if (borrow == -1)
{
// If the head data is 0, then
// update it with 9 and return -1
if (head.data == 0)
{
head.data = 9;
return -1;
}
// Otherwise, decrement head's
// data by 1 and return 0
else
{
head.data = head.data - 1;
return 0;
}
}
// Otherwise, return 0
else
{
return 0;
}
}
// Function to subtract 1 from the given
// Linked List representation of number
static Node subtractOne(Node head)
{
// Recursively subtract 1 from
// the Linked List
subtractOneUtil(head);
// Increment the head pointer
// if there are any leading zeros
while (head != null && head.next != null &&
head.data == 0)
{
head = head.next;
}
return head;
}
// Function to print a linked list
static void printList(Node node)
{
// Iterate until node is null
while (node != null)
{
System.out.print(node.data);
node = node.next;
}
System.out.println();
}
// Driver Code
public static void main(String[] args)
{
Node head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
System.out.print("List is ");
printList(head);
head = subtractOne(head);
System.out.print("Resultant list is ");
printList(head);
}
}
// This code is contributed by 29AjayKumar
# Python3 program for the above approach
# Linked list Node
class Node:
def __init__(self, d):
self.data = d
self.next = None
# Recursive function to subtract 1
# from the linked list and update
# the node value accordingly
def subtractOneUtil(head):
# Base Case
if (head == None):
return -1
# Recursively call for the next
# node of the head
borrow = subtractOneUtil(head.next)
# If there is a borrow
if (borrow == -1):
# If the head data is 0, then
# update it with 9 and return -1
if (head.data == 0):
head.data = 9
return -1
# Otherwise, decrement head's
# data by 1 and return 0
else:
head.data = head.data - 1
return 0
# Otherwise, return 0
else:
return 0
# Function to subtract 1 from the given
# Linked List representation of number
def subtractOne(head):
# Recursively subtract 1 from
# the Linked List
subtractOneUtil(head)
# Increment the head pointer
# if there are any leading zeros
while (head and head.next and
head.data == 0):
head = head.next
return head
# Function to print a linked list
def printList(node):
# Iterate until node is None
while (node != None):
print(node.data, end = "")
node = node.next
print()
# Driver Code
if __name__ == '__main__':
head = Node(1)
head.next = Node(0)
head.next.next = Node(0)
head.next.next.next = Node(0)
print("List is ", end = "")
printList(head)
head = subtractOne(head)
print("Resultant list is ", end = "")
printList(head)
# This code is contributed by mohit kumar 29
// C# program for the above approach
using System;
class GFG{
// Linked list Node
class Node
{
public int data;
public Node next;
};
// Function to create a new node with
// the given data
static Node newNode(int data)
{
// Create a new node
Node new_node = new Node();
new_node.data = data;
new_node.next = null;
// Return the created node
return new_node;
}
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
static int subtractOneUtil(Node head)
{
// Base Case
if (head == null)
return -1;
// Recursively call for the next
// node of the head
int borrow = subtractOneUtil(
head.next);
// If there is a borrow
if (borrow == -1)
{
// If the head data is 0, then
// update it with 9 and return -1
if (head.data == 0)
{
head.data = 9;
return -1;
}
// Otherwise, decrement head's
// data by 1 and return 0
else
{
head.data = head.data - 1;
return 0;
}
}
// Otherwise, return 0
else
{
return 0;
}
}
// Function to subtract 1 from the given
// Linked List representation of number
static Node subtractOne(Node head)
{
// Recursively subtract 1 from
// the Linked List
subtractOneUtil(head);
// Increment the head pointer
// if there are any leading zeros
while (head != null && head.next != null &&
head.data == 0)
{
head = head.next;
}
return head;
}
// Function to print a linked list
static void printList(Node node)
{
// Iterate until node is null
while (node != null)
{
Console.Write(node.data);
node = node.next;
}
Console.WriteLine();
}
// Driver Code
public static void Main()
{
Node head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
Console.Write("List is ");
printList(head);
head = subtractOne(head);
Console.Write("Resultant list is ");
printList(head);
}
}
// This code is contributed by SURENDRA_GANGWAR
<script>
// JavaScript program for the above approach
// Linked list Node
class Node
{
constructor()
{
this.next = null;
}
}
// Function to create a new node with
// the given data
function newNode(data)
{
// Create a new node
let new_node = new Node();
new_node.data = data;
new_node.next = null;
// Return the created node
return new_node;
}
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
function subtractOneUtil(head)
{
// Base Case
if (head == null)
return -1;
// Recursively call for the next
// node of the head
let borrow = subtractOneUtil(head.next);
// If there is a borrow
if (borrow == -1)
{
// If the head data is 0, then
// update it with 9 and return -1
if (head.data == 0)
{
head.data = 9;
return -1;
}
// Otherwise, decrement head's
// data by 1 and return 0
else
{
head.data = head.data - 1;
return 0;
}
}
// Otherwise, return 0
else
{
return 0;
}
}
// Function to subtract 1 from the given
// Linked List representation of number
function subtractOne(head)
{
// Recursively subtract 1 from
// the Linked List
subtractOneUtil(head);
// Increment the head pointer
// if there are any leading zeros
while (head != null && head.next != null &&
head.data == 0)
{
head = head.next;
}
return head;
}
// Function to print a linked list
function printList(node)
{
// Iterate until node is null
while (node != null)
{
document.write(node.data);
node = node.next;
}
document.write("<br>");
}
// Driver Code
let head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
document.write("List is ");
printList(head);
head = subtractOne(head);
document.write("Resultant list is ");
printList(head);
// This code is contributed by Dharanendra L V.
</script>
OutputList is 1000
Resultant list is 999
Time Complexity: O(N), N is the length of the given linked list.
Auxiliary Space: O(1)
New Approach by reverse the linked list :
- Subtract 1 from the first node (i.e., the ones place), and then handle the carry if require.
- .Then, reverse the linked list back to its original form and return the updated linked list.
Below is the implementation of the above approach:
C++
// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
// Linked list Node
class Node {
public:
int data;
Node* next;
};
// Function to create a new node with
// the given data
Node* newNode(int data)
{
// Create a new node
Node* new_node = new Node;
new_node->data = data;
new_node->next = NULL;
// Return the created node
return new_node;
}
// Function to reverse a linked list
Node* reverseList(Node* head)
{
Node *prev = NULL, *curr = head, *next;
while (curr != NULL) {
next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
return prev;
}
// Function to subtract 1 from the given
// Linked List representation of number
Node* subtractOne(Node* head)
{
// Reverse the linked list
head = reverseList(head);
// Subtract 1 from the first node
head->data -= 1;
// Handle the carry if required
Node* curr = head;
while (curr->data < 0) {
curr->data += 10;
if (curr->next == NULL) {
curr->next = newNode(0);
}
curr->next->data -= 1;
curr = curr->next;
}
// Reverse the linked list back to
// its original form
head = reverseList(head);
// Increment the head pointer
// if there are any leading zeros
while (head and head->next and head->data == 0) {
head = head->next;
}
return head;
}
// Function to print a linked list
void printList(Node* node)
{
// Iterate until node is NULL
while (node != NULL) {
cout << node->data;
node = node->next;
}
cout << endl;
}
// Driver Code
int main()
{
Node* head = newNode(1);
head->next = newNode(0);
head->next->next = newNode(0);
head->next->next->next = newNode(0);
cout << "List is ";
printList(head);
head = subtractOne(head);
cout << "Resultant list is ";
printList(head);
return 0;
}
//This code is contributed by chinmaya121221
public class Main {
// Linked list Node
static class Node {
int data;
Node next;
}
// Function to create a new node with
// the given data
static Node newNode(int data)
{
// Create a new node
Node new_node = new Node();
new_node.data = data;
new_node.next = null;
// Return the created node
return new_node;
}
// Function to reverse a linked list
static Node reverseList(Node head) {
Node prev = null, curr = head, next;
while (curr != null) {
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
// Function to subtract 1 from the given
// Linked List representation of number
static Node subtractOne(Node head) {
// Reverse the linked list
head = reverseList(head);
// Subtract 1 from the first node
head.data -= 1;
// Handle the carry if required
Node curr = head;
while (curr.data < 0) {
curr.data += 10;
if (curr.next == null) {
curr.next = newNode(0);
}
curr.next.data -= 1;
curr = curr.next;
}
// Reverse the linked list back to
// its original form
head = reverseList(head);
// Increment the head pointer
// if there are any leading zeros
while (head != null && head.next != null && head.data == 0) {
head = head.next;
}
return head;
}
// Function to print a linked list
static void printList(Node node) {
// Iterate until node is NULL
while (node != null) {
System.out.print(node.data);
node = node.next;
}
System.out.println();
}
public static void main(String[] args) {
Node head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
System.out.print("List is ");
printList(head);
head = subtractOne(head);
System.out.print("Resultant list is ");
printList(head);
}
}
# Linked list Node
class Node:
def __init__(self, data):
self.data = data
self.next = None
# Function to create a new node with the given data
def newNode(data):
# Create a new node
new_node = Node(data)
# Return the created node
return new_node
# Function to reverse a linked list
def reverseList(head):
prev = None
curr = head
next = None
while curr != None:
next = curr.next
curr.next = prev
prev = curr
curr = next
return prev
# Function to subtract 1 from the given
# Linked List representation of number
def subtractOne(head):
# Reverse the linked list
head = reverseList(head)
# Subtract 1 from the first node
head.data -= 1
# Handle the carry if required
curr = head
while curr.data < 0:
curr.data += 10
if curr.next == None:
curr.next = newNode(0)
curr.next.data -= 1
curr = curr.next
# Reverse the linked list back to its original form
head = reverseList(head)
# Increment the head pointer if there are any leading zeros
while head and head.next and head.data == 0:
head = head.next
return head
# Function to print a linked list
def printList(node):
# Iterate until node is NULL
while node != None:
print(node.data, end="")
node = node.next
print()
# Driver Code
head = newNode(1)
head.next = newNode(0)
head.next.next = newNode(0)
head.next.next.next = newNode(0)
print("List is ")
printList(head)
head = subtractOne(head)
print("Resultant list is ")
printList(head)
// C# program for the above approach
using System;
// Linked list Node
class Node {
public int data;
public Node next;
};
// Main class
class MainClass {
// Function to create a new node with
// the given data
static Node newNode(int data)
{
// Create a new node
Node new_node = new Node();
new_node.data = data;
new_node.next = null;
// Return the created node
return new_node;
}
// Function to reverse a linked list
static Node reverseList(Node head)
{
Node prev = null, curr = head, next;
while (curr != null) {
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
// Function to subtract 1 from the given
// Linked List representation of number
static Node subtractOne(Node head)
{
// Reverse the linked list
head = reverseList(head);
// Subtract 1 from the first node
head.data -= 1;
// Handle the carry if required
Node curr = head;
while (curr.data < 0) {
curr.data += 10;
if (curr.next == null) {
curr.next = newNode(0);
}
curr.next.data -= 1;
curr = curr.next;
}
// Reverse the linked list back to
// its original form
head = reverseList(head);
// Increment the head pointer
// if there are any leading zeros
while (head != null && head.next != null
&& head.data == 0) {
head = head.next;
}
return head;
}
// Function to print a linked list
static void printList(Node node)
{
// Iterate until node is NULL
while (node != null) {
Console.Write(node.data);
node = node.next;
}
Console.WriteLine();
}
// Driver Code
public static void Main()
{
Node head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
Console.Write("List is ");
printList(head);
head = subtractOne(head);
Console.Write("Resultant list is ");
printList(head);
}
}
// This code is contributed by rutikbhosale
// Linked list Node
class Node {
constructor(data) {
this.data = data;
this.next = null;
}
}
// Function to create a new node with the given data
function newNode(data)
{
// Create a new node
let new_node = new Node(data);
// Return the created node
return new_node;
}
// Function to reverse a linked list
function reverseList(head) {
let prev = null,
curr = head,
next;
while (curr != null) {
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
// Function to subtract 1 from the given
// Linked List representation of number
function subtractOne(head) {
// Reverse the linked list
head = reverseList(head);
// Subtract 1 from the first node
head.data -= 1;
// Handle the carry if required
let curr = head;
while (curr.data < 0) {
curr.data += 10;
if (curr.next == null) {
curr.next = newNode(0);
}
curr.next.data -= 1;
curr = curr.next;
}
// Reverse the linked list back to its original form
head = reverseList(head);
// Increment the head pointer if there are any leading zeros
while (head && head.next && head.data == 0) {
head = head.next;
}
return head;
}
// Function to print a linked list
function printList(node) {
// Iterate until node is NULL
while (node != null) {
process.stdout.write(node.data + "");
node = node.next;
}
console.log();
}
// Driver Code
let head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
console.log("List is ");
printList(head);
head = subtractOne(head);
console.log("Resultant list is ");
printList(head);
OutputList is 1000
Resultant list is 999
Time Complexity: O(n), where n is the length of the linked list.
Space Complexity: O(n), where n is the length of the linked list.
Another approach using Stack:
C++
#include <bits/stdc++.h>
using namespace std;
// Linked list Node
class Node {
public:
int data;
Node* next;
};
// Function to create a new node with
// the given data
Node* newNode(int data)
{
// Create a new node
Node* new_node = new Node;
new_node->data = data;
new_node->next = NULL;
// Return the created node
return new_node;
}
// Function to subtract 1 from the given
// Linked List representation of number using stack
Node* subtractOne(Node* head)
{
stack<int> s;
// Traverse the linked list and push values onto the stack
Node* curr = head;
while (curr != NULL) {
s.push(curr->data);
curr = curr->next;
}
int borrow = 1;
Node* new_head = NULL;
// Pop elements from the stack and subtract borrow
while (!s.empty()) {
int val = s.top() - borrow;
borrow = 0;
if (val < 0) {
val += 10;
borrow = 1;
}
s.pop();
Node* new_node = newNode(val);
new_node->next = new_head;
new_head = new_node;
}
// Remove leading zeros
while (new_head != NULL && new_head->data == 0) {
Node* temp = new_head;
new_head = new_head->next;
delete temp;
}
return new_head;
}
// Function to print a linked list
void printList(Node* node)
{
// Iterate until node is NULL
while (node != NULL) {
cout << node->data;
node = node->next;
}
cout << endl;
}
// Nikunj Sonigara
// Driver Code
int main()
{
Node* head = newNode(1);
head->next = newNode(0);
head->next->next = newNode(0);
head->next->next->next = newNode(0);
cout << "List is ";
printList(head);
head = subtractOne(head);
cout << "Resultant list is ";
printList(head);
return 0;
}
import java.util.Stack;
// Linked list Node
class Node {
int data;
Node next;
Node(int data)
{
this.data = data;
this.next = null;
}
}
public class Main {
// Function to subtract 1 from the given
// Linked List representation of number using stack
static Node subtractOne(Node head)
{
Stack<Integer> s = new Stack<>();
// Traverse the linked list and push values onto the
// stack
Node curr = head;
while (curr != null) {
s.push(curr.data);
curr = curr.next;
}
int borrow = 1;
Node new_head = null;
// Pop elements from the stack and subtract borrow
while (!s.empty()) {
int val = s.pop() - borrow;
borrow = 0;
if (val < 0) {
val += 10;
borrow = 1;
}
Node new_node = new Node(val);
new_node.next = new_head;
new_head = new_node;
}
// Remove leading zeros
while (new_head != null && new_head.data == 0) {
Node temp = new_head;
new_head = new_head.next;
temp = null;
}
return new_head;
}
// Function to print a linked list
static void printList(Node node)
{
// Iterate until node is null
while (node != null) {
System.out.print(node.data);
node = node.next;
}
System.out.println();
}
// Driver Code
public static void main(String[] args)
{
Node head = new Node(1);
head.next = new Node(0);
head.next.next = new Node(0);
head.next.next.next = new Node(0);
System.out.print("List is ");
printList(head);
head = subtractOne(head);
System.out.print("Resultant list is ");
printList(head);
}
}
# Linked list Node
class Node:
def __init__(self, data):
self.data = data
self.next = None
# Function to create a new node with the given data
def new_node(data):
# Create a new node
new_node = Node(data)
# Return the created node
return new_node
# Function to subtract 1 from the given Linked List representation of number using stack
def subtract_one(head):
stack = []
# Traverse the linked list and push values onto the stack
curr = head
while curr is not None:
stack.append(curr.data)
curr = curr.next
borrow = 1
new_head = None
# Pop elements from the stack and subtract borrow
while stack:
val = stack.pop() - borrow
borrow = 0
if val < 0:
val += 10
borrow = 1
new_node = Node(val)
new_node.next = new_head
new_head = new_node
# Remove leading zeros
while new_head is not None and new_head.data == 0:
temp = new_head
new_head = new_head.next
del temp
return new_head
# Function to print a linked list
def print_list(node):
# Iterate until node is None
while node is not None:
print node.data, # Adding a comma to suppress the newline character
node = node.next
print # Print a newline after the loop
# Driver Code
if __name__ == "__main__":
head = new_node(1)
head.next = new_node(0)
head.next.next = new_node(0)
head.next.next.next = new_node(0)
print "List is ",
print_list(head)
head = subtract_one(head)
print "Resultant list is ",
print_list(head)
# Contributed by sinudp5vi
using System;
using System.Collections.Generic;
// Linked list Node
class Node {
public int data;
public Node next;
}
class GFG {
// Function to create a new node with
// the given data
static Node NewNode(int data)
{
// Create a new node
Node new_node = new Node();
new_node.data = data;
new_node.next = null;
// Return the created node
return new_node;
}
// Function to subtract 1 from the given
// Linked List representation of number using stack
static Node SubtractOne(Node head)
{
Stack<int> stack = new Stack<int>();
// Traverse the linked list and push values onto the
// stack
Node curr = head;
while (curr != null) {
stack.Push(curr.data);
curr = curr.next;
}
int borrow = 1;
Node new_head = null;
// Pop elements from the stack and subtract borrow
while (stack.Count > 0) {
int val = stack.Pop() - borrow;
borrow = 0;
if (val < 0) {
val += 10;
borrow = 1;
}
Node new_node = NewNode(val);
new_node.next = new_head;
new_head = new_node;
}
// Remove leading zeros
while (new_head != null && new_head.data == 0) {
new_head = new_head.next;
}
return new_head;
}
// Function to print a linked list
static void PrintList(Node node)
{
// Iterate until node is null
while (node != null) {
Console.Write(node.data);
node = node.next;
}
Console.WriteLine();
}
// Driver code
static void Main()
{
Node head = NewNode(1);
head.next = NewNode(0);
head.next.next = NewNode(0);
head.next.next.next = NewNode(0);
Console.Write("List is ");
PrintList(head);
head = SubtractOne(head);
Console.Write("Resultant list is ");
PrintList(head);
}
}
// Linked list Node
class Node {
constructor(data) {
this.data = data;
this.next = null;
}
}
// Function to create a new node with the given data
function new_node(data) {
// Create a new node
const new_node = new Node(data);
// Return the created node
return new_node;
}
// Function to subtract 1 from the given Linked List representation of number using stack
function subtract_one(head) {
const stack = [];
// Traverse the linked list and push values onto the stack
let curr = head;
while (curr !== null) {
stack.push(curr.data);
curr = curr.next;
}
let borrow = 1;
let new_head = null;
// Pop elements from the stack and subtract borrow
while (stack.length > 0) {
let val = stack.pop() - borrow;
borrow = 0;
if (val < 0) {
val += 10;
borrow = 1;
}
const new_node = new Node(val);
new_node.next = new_head;
new_head = new_node;
}
// Remove leading zeros
while (new_head !== null && new_head.data === 0) {
const temp = new_head;
new_head = new_head.next;
// Delete temp (Not required in JavaScript as memory management is automatic)
}
return new_head;
}
// Function to print a linked list
function print_list(node) {
// Iterate until node is null
while (node !== null) {
console.log(node.data);
node = node.next;
}
}
// Driver Code
const head = new_node(1);
head.next = new_node(0);
head.next.next = new_node(0);
head.next.next.next = new_node(0);
console.log("List is:");
print_list(head);
const newHead = subtract_one(head);
console.log("Resultant list is:");
print_list(newHead);
OutputList is 1000
Resultant list is 999
Time Complexity: O(n)
Space Complexity: O(n)
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