160. 相交鏈表（同劍指offer,兩個鏈表的公共節點）

 

---

/**
 * 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==NULL||headB==NULL)return NULL;
        //運用兩個指針遍歷兩個鏈表，如果兩個鏈表相交即會有指向同一個節點，
        ListNode*P_A=headA;
        ListNode*P_B=headB;
        int count=0;//用來標記是否已經超過兩次爲空，超過即不會相交
        while(count<=2)
        {
            if(P_A==P_B)return P_A;
            P_A=P_A->next;
            P_B=P_B->next;
            //指向爲空了，交換鏈表遍歷
            if(P_A==NULL)
            {
                P_A=headB;
                count++;
            }
                
            if(P_B==NULL)
            {
                P_B=headA;
                count++;
            }        
        }

        return NULL;
    }
};

---

/**
 * 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) {
        ListNode* A = headA, *B = headB;
        while(A || B) {
            if(A == B)
                return A;
            if(A)
                A = A->next;
            else
                A = headB;
            if(B)
                B = B->next;
            else
                B = headA;
        }
        return NULL;
    }
};