[剑指 offer] JT36---The first common node of two linked lists (what's the difference between finding the same value with an array?)

The topic is as follows

Idea and code

I saw that there is a way to calculate the length of two linked lists. I didn't understand it. I just saved one in the map and checked the other. I was superficial. . . Directly!

/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
    
    
public:
    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
    
    
        ListNode* cur=pHead1;
        map<int,bool> m;
        for(;cur!=NULL;cur=cur->next){
    
    
            m[cur->val]=true;
        }
        for(cur=pHead2;cur!=NULL;cur=cur->next){
    
    
            if(m.find(cur->val)!=m.end()){
    
    
                return cur;
            }
        }
        return NULL;
    }
};