###### tags: `leetcode`
# Question No.160:
### Description:
Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:


begin to intersect at node c1.

Given a pattern and a string s, find if s follows the same pattern.

Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in s.
### Solution:
Use **_ordered_set_** to store already exist items
### AC code

/*struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};*/

class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        if(headA==NULL || headB==NULL)
            return NULL;
        unordered_set<ListNode* > A; 
        ListNode *taila;
        ListNode *tailb;
        taila = headA;
        tailb = headB;

        while(taila!=NULL){
            A.insert(taila);
            taila = taila->next;
        }
        
        while(tailb!=NULL){
            if(A.find(tailb)!=A.end()){
                return tailb;
            }
            tailb = tailb->next;
        }
        return NULL;
    }
};