Merge pull request #681 from geekySapien/geekysapien

Added a C++ solution for add 1 to a number represented by linked list

Author: smv1999

Data Structures/Linked Lists/Singly Linked List/add_one_to_number_represented_by_linkedlist.cpp

@@ -0,0 +1,184 @@
+//Link to Problem:  https://practice.geeksforgeeks.org/problems/add-1-to-a-number-represented-as-linked-list/1
+
+//Problem Description: We need to add 1 to a number represented as Linked List
+
+//Sample Test Cases
+
+/*
+
+Test Case 1
+
+If the linked list given is as follows
+
+4 -> 5 -> 6
+
+We need to return this linked list as output
+
+4 -> 5 -> 7
+
+*/
+
+/*
+
+Test Case 2
+
+If the linked list given is as follows
+
+9 -> 9 -> 9
+
+We need to return this linked list as output
+
+1 -> 0 -> 0 -> 0
+
+
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+//Structure of Linked List
+struct Node
+{
+    int data;
+    struct Node *next;
+
+    Node(int x)
+    {
+        data = x;
+        next = NULL;
+    }
+};
+
+// Function to display a linked list
+void printList(Node *node)
+{
+    while (node != NULL)
+    {
+        cout << node->data;
+        node = node->next;
+    }
+    cout << "\n";
+}
+
+class Solution
+{
+public:
+    // A utility function to reverse a linked list
+    Node *reverse(Node *head)
+    {
+        Node *curr = head;
+        Node *next = NULL;
+        Node *prev = NULL;
+        while (curr != NULL)
+        {
+            next = curr->next;
+            curr->next = prev;
+            prev = curr;
+            curr = next;
+        }
+        return prev;
+    }
+
+    // Function to add 1 to a number represented as linked list
+    Node *addOne(Node *head)
+    {
+        // we first reverse the linked list
+        head = reverse(head);
+
+        // we create a boolean variable whether 1 is added to the number or not.
+        //If it is true, we assume, we need to add 1 in the number (so we make
+        //it true by default)
+        //when 1 is added to the number, we will make it false
+        bool f = true;
+
+        //curr refers to the current pointer which points to the head of the
+        //linked list
+        Node *curr = head;
+
+        // we iterate till we reach the end of linked list OR we added 1 to the
+        // linked list OR Both is some case (as described in test case 2)
+        while (curr != NULL && f == true)
+        {
+
+            //This is the condition that would be executed when we have numbers
+            //like 9, 99, 999, 9999 and so on
+
+            //Here next pointer of current would be null and the data of current
+            //pointer would be 9
+            if (curr->next == NULL && curr->data == 9)
+            {
+                // we make the data value of current pointer to 1
+                curr->data = 1;
+
+                // we make a new node called temp with value 0 (because we need
+                // to have 1 extra 0 for example in case of 9 <- 9 <- 9, we make the
+                // current value to 1 and the list would look like 1 <- 0 <- 0
+                Node *temp = new Node(0);
+
+                // we add that zero before the head, this will make the linked
+                // list as  1 <- 0 <- 0 <- 0
+                temp->next = head;
+
+                // we make temp as the head of the linked list
+                head = temp;
+
+                //we point current pointer to its next node which will make
+                //curr point to NULL and will exit from the while loop
+                curr = curr->next;
+            }
+
+            //This is the case that would be executed when we have numbers like
+            //19, 119, etc (i.e 9 is present on the LSB(least significant bit) of original number )
+            else if (curr->data == 9)
+            {
+                // we make the value of current pointer to 0 and move to next node
+                curr->data = 0;
+                curr = curr->next;
+            }
+
+            //This is the trivial case that would be executed for numbers like 5
+            //16, 456 etc
+            else
+            {
+
+                // we increment the value of current's pointer by 1.
+                curr->data = curr->data + 1;
+
+                // we make f false so as to terminate the while loop
+                f = false;
+
+                //move the current pointer to its next node
+                curr = curr->next;
+            }
+        }
+
+        //we reverse the reversed linked list to obtain the original linked list
+        head = reverse(head);
+
+        // we finally return the head of new linked list
+        return head;
+    }
+};
+
+int main()
+{
+    int t;
+    cin >> t;
+    while (t--)
+    {
+        string s;
+        cin >> s;
+
+        Node *head = new Node(s[0] - '0');
+        Node *tail = head;
+        for (int i = 1; i < s.size(); i++)
+        {
+            tail->next = new Node(s[i] - '0');
+            tail = tail->next;
+        }
+        Solution ob;
+        head = ob.addOne(head);
+        printList(head);
+    }
+    return 0;
+}