两个链表的第一个公共节点

class Solution {
public:
    ListNode* FindFirstCommonNode( ListNode *pHead1, ListNode *pHead2) {
        int size1=0,size2=0;
        ListNode* p1=pHead1;
        ListNode* p2=pHead2;
        while(pHead1!=NULL){
            size1++;
            pHead1=pHead1->next;
        }
        while(pHead2!=NULL){
            size2++;
            pHead2=pHead2->next;
        }
        pHead1=p1;
        pHead2=p2;
        if(size1>size2){
            int n=size1-size2;
            while(n--)
                pHead1=pHead1->next;
        }
        else if(size1<size2){
            int m=size2-size1;
            while(m--)
                pHead2=pHead2->next;
        }
        while(pHead1!=pHead2 &&pHead1!=NULL && pHead2!=NULL){
            pHead1=pHead1->next;
            pHead2=pHead2->next;
        }
        return pHead1;
    }
};