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暴力遍历：

/** * 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 *curA=headA,*curB=headB;        while(curA!=nullptr){
               while(curB!=nullptr){
                   if(curB==curA)                    return curA;                curB = curB->next;            }            curA=curA->next;            curB = headB;        }        return nullptr;    }};

Hash表：

/** * 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 *curA=headA,*curB=headB;        unordered_set
   
     data;        while(curA!=nullptr){
               data.insert(curA);            curA=curA->next;        }        while(curB!=nullptr){
               if(data.find(curB)!=data.end())                return curB;            curB = curB->next;        }        return nullptr;    }};
   

双指针：

/** * 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 *curA=headA,*curB=headB;        bool signA=true,signB=true;        while(curA!=nullptr||curB!=nullptr){
               if(curA==curB&&curA!=nullptr)                return curA;            curA = curA->next;            curB = curB->next;            if(curA==nullptr&&signA){
                   curA=headB;                signA=false;            }            if(curB==nullptr&&signB){
                   curB=headA;                signB=false;            }        }        return nullptr;    }};

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