Description

Submission

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        unordered_map<ListNode*, int> m;
        for(ListNode* node = headA; node; node = node->next) {
            m[node] = 1;
        }
        for(ListNode* node = headB; node; node = node->next) {
            if(m.find(node) != m.end()) return node;
        }
        return NULL;
    }
};

Submission 210604

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        if(headA == nullptr || headB == nullptr) {
            return nullptr;
        }

        ListNode* pA = headA, *pB = headB;

        while(pA != pB) {
            pA = pA == nullptr ? headB : pA->next;
            pB = pB == nullptr ? headA : pB->next;
        }

        return pA;
    }
};