35 两个链表的第一个公共结点

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
        if(pHead1 == nullptr || pHead2 == nullptr){
            return nullptr;
        }
        ListNode* p1 = pHead1,*p2 = pHead2;
        int len1 = 0,len2 = 0;
        while(p1 != nullptr){
            ++len1;
            p1 = p1 -> next;
        }
        while(p2 != nullptr){
            ++len2;
            p2 = p2 -> next;
        }
        p1 = pHead1;
        p2 = pHead2;
        if(len1 < len2){
             p1 = pHead2;
             p2 = pHead1;
        }
        for(int i = 0;i < abs(len1 - len2);++i){
            p1 = p1 -> next;
        }
        while(p1 != nullptr && p2 != nullptr){
            if(p1 -> val == p2 -> val){
                return p1;
            }
            else{
                p1 = p1 -> next;
                p2 = p2 -> next;
            }
        }
        return nullptr;
    }
};