题解 | #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:
    int ListLength(ListNode* plist) {
        int n = 0;
        while (plist != nullptr) {
            plist = plist->next;
            n++;
        }
        return n;
    }
    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
        int len1 = ListLength(pHead1);
        int len2 = ListLength(pHead2);
        int n = abs(len1 - len2);

        if (len1 >= len2) {
            for (int i = 0; i < n; i++) pHead1 = pHead1->next;
        } else {
            for (int i = 0; i < n; i++) pHead2 = pHead2->next;
        }

        while ((pHead1 != nullptr) && (pHead2 != nullptr) && (pHead1 != pHead2)) {
            pHead1 = pHead1->next;
            pHead2 = pHead2->next;
        }

        return pHead1;
    }
};