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两个链表的第一个公共结点

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输入两个链表，找出它们的第一个公共结点。

长度差、快慢指针

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/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    int get_length(const ListNode* pHead)
    {
        int len = 0;
        while (pHead != nullptr)
        {
            pHead = pHead->next;
            len++;
        }
        return len;
    }
    ListNode* FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2) {
        int a = get_length(pHead1);
        int b = get_length(pHead2);
        if (a < b)
        {
            int d = b - a;
            for (int i = 0; i < d; i++)
            {
                pHead2 = pHead2->next;
            }
        }
        else
        {
            int d = a - b;
            for (int i = 0; i < d; i++)
            {
                pHead1 = pHead1->next;
            }
        }
        while (pHead1 != pHead2)
        {
            if (pHead1 == nullptr || pHead2 == nullptr)
            {
                return nullptr;
            }
            else
            {
                pHead1 = pHead1->next;
                pHead2 = pHead2->next;
            }
        }
        return pHead1;
    }
};