lec5_6.cpp

//{ Driver Code Starts
#include <iostream>

#include <bits/stdc++.h>
using namespace std;

/* Link list Node */
struct Node {
    int data;
    struct Node* next;

    Node(int x) {
        data = x;
        next = NULL;
    }
};

vector<int> take() {
    vector<int> arr;
    string input;
    getline(cin, input);
    stringstream ss(input);
    int number;
    while (ss >> number) {
        arr.push_back(number);
    }
    return arr;
}

Node* inputList(int size, vector<int> v) {
    if (size == 0)
        return NULL;

    int val = v[0];

    Node* head = new Node(val);
    Node* tail = head;

    for (int i = 0; i < size - 1; i++) {
        val = v[i + 1];
        tail->next = new Node(val);
        tail = tail->next;
    }

    return head;
}


// } Driver Code Ends
/* Linked List Node
struct Node {
  int data;
  struct Node *next;
  Node(int x) {
    data = x;
    next = NULL;
  }
}; */

class Solution {
  public:
    // Function to find intersection point in Y shaped Linked Lists.
    int intersectPoint(Node* head1, Node* head2) {
        // Your Code Here
        
        // Pointing curr1 to the head , travese to end and point to head 
        Node *curr1 = head1;
        
        while(curr1->next)
        {
            curr1 = curr1->next;
        }
        
        curr1->next = head1;
        
        Node *slow = head2 , *fast = head2;
        
        while(fast && fast->next)
        {
            slow = slow->next;
            fast = fast->next->next;
            
            if(slow == fast)
            {
                break;
            }
        }
        
        if(!fast || !fast->next) // not connected
        {
            return -1;
        }
        
        slow = head2;
        
        while(slow!= fast)
        {
            slow = slow->next;
            fast = fast->next;
        }
        
        
        return slow->data;
        
        
    }
};


//{ Driver Code Starts.

/* Driver program to test above function*/
int main() {
    srand(time(0));
    int T, n1, n2, n3;

    cin >> T;
    cin.ignore();
    while (T--) {

        vector<int> v1 = take();
        vector<int> v2 = take();
        vector<int> v3 = take();
        int n1 = v1.size(), n2 = v2.size(), n3 = v3.size();

        Node* head1 = NULL;
        Node* head2 = NULL;
        Node* common = NULL;

        head1 = inputList(n1, v1);
        head2 = inputList(n2, v2);
        common = inputList(n3, v3);

        Node* temp = head1;
        while (temp != NULL && temp->next != NULL)
            temp = temp->next;
        if (temp != NULL)
            temp->next = common;

        temp = head2;
        while (temp != NULL && temp->next != NULL)
            temp = temp->next;
        if (temp != NULL)
            temp->next = common;
        Solution ob;
        cout << ob.intersectPoint(head1, head2) << endl;
    }
    return 0;
}

// } Driver Code Ends