剑指offer 36：两个链表的第一个公共节点

#include <iostream>
struct ListNode
{
public:
    int val;
    struct ListNode *next;
};
using namespace std;
class solution
{
public:
    
    //36 找到两个链表的第一个公共节点
    
    //让长的一个链表先走，实现右对齐
    ListNode* FindFirstCommonNode(ListNode *leftHead ,ListNode *rightHead) {
        ListNode *left = leftHead;
        ListNode *right = rightHead;
        int leftLength = 0;
        int rightLength = 0;
        leftLength = GetListLength(left);
        rightLength = GetListLength(right);

        int length = 0;
        if (leftLength < rightLength) {
            length = rightLength - leftLength;
            while (right != NULL && length > 0) {
                right = right->next;
                length--;
            }
        }//右先走

        else {
            length = leftLength - rightLength;
            while(left != NULL && length > 0) {
                left = left->next;
                length--;
            }
        }//左先走

        while (left != NULL && right !=NULL) {
            if (left == right) {
                break;
            }
            left = left->next;
            right = right->next;
        }//一起走，直到相遇

        return ((left == right) ? left : NULL);
    }

    int GetListLength(ListNode *head) {
        ListNode *node = head;
        int length = 0;
        while (node != NULL) {
            length++;
            node = node->next;
        }
        return length;
    }
    
    
    //遍历
    //拼接起来右对齐
    //栈youduiqi
    //map ，hashmap
};

int main()
{
    ListNode common[2];
    common[0].val = 8;
    common[0].next = &common[1];

    common[1].val = 9;
    common[1].next = NULL;



    ListNode list[4];
    list[0].val = 1;
    list[0].next = &list[1];

    list[1].val = 2;
    list[1].next = &list[2];

    list[2].val = 3;
    list[2].next = &list[3];
    list[3].val = 4;
    list[3].next = &common[0];

    ListNode list2[2];
    list2[0].val = 5;
    list2[0].next = &list2[1];

    list2[1].val = 6;
    list2[1].next = &common[0];




    solution solu;
    ListNode *node = solu.FindFirstCommonNode(list, list2);
    while (node != NULL) {
        cout << node->val << endl;
        node = node->next;
    }
    return 0;
}