剑指Offer-35.两个链表的第一个公共结点(C++/Java)

class Solution {
public:
    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
        int d1 = 0;
        int d2 = 0;
        int d = 0;
        ListNode* p1 = pHead1;
        ListNode* p2 = pHead2;
        while(p1 != nullptr){
            p1 = p1->next;
            d1++;
        }
        while(p2 != nullptr){
            p2 = p2->next;
            d2++;
        }
        if(d1 < d2){
            d = d2 - d1;
            while(d--){
                pHead2 = pHead2->next;
            }
        }
        else{
            d = d1 - d2;
            while(d--){
                pHead1 = pHead1->next;
            }
        }
        while(pHead1 != nullptr && pHead2 != nullptr){
            if(pHead1 == pHead2){
                return pHead1;
            }
            pHead1 = pHead1->next;
            pHead2 = pHead2->next;
        }
        return nullptr;
    }
};

public class Solution {
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
        int d1 = 0;
        int d2 = 0;
        int d = 0;
        ListNode p1 = pHead1;
        ListNode p2 = pHead2;
        while(p1 != null){
            p1 = p1.next;
            d1++;
        }
        while(p2 != null){
            p2 = p2.next;
            d2++;
        }
        if(d1 < d2){
            d = d2 - d1;
            while(d-- != 0){
                pHead2 = pHead2.next;
            }
        }
        else{
            d = d1 - d2;
            while(d-- != 0){
                pHead1 = pHead1.next;
            }
        }
        while(pHead1 != null && pHead2 != null){
            if(pHead1 == pHead2){
                return pHead1;
            }
            pHead1 = pHead1.next;
            pHead2 = pHead2.next;
        }
        return null;
    }
}