单链表判断是否相交

判断单链表是否有环路可以参考：单链表判断环路及环路的入口

typedef int DataType;//节点中数据类型typedef struct ListNode//节点数据结构{    DataType data;    struct ListNode *next;} ListNode;typedef struct CheckNoode/{    int flag;    ListNode *p1;    ListNode *p2;} CheckNoode;

1.判断两个链表是否相交，若相交，求交点。（假设不带环）

//判断是否相交bool CheckIsMeet(ListNode *plist1,ListNode *plist2){    while (plist1->next != NULL)    {        plist1 = plist1->next;    }    while (plist2->next != NULL)    {        plist2 = plist2->next;    }    if (plist1 == plist2)    {        return true;    }    else    {        return false;    }}

//若相交，求交点ListNode *AnswerMeetNode(ListNode *plist1,ListNode *plist2){    int count1 = 0;    int count2 = 0;    int count = 0;    ListNode *cur1 = plist1;    ListNode *cur2 = plist2;    while (cur1 != NULL)    {        count1++;        cur1 = cur1->next;    }    while (cur2 != NULL)    {        count2++;        cur2 = cur2->next;    }    count = count1 - count2;    if (count > 0)    {        while (count--)        {            plist1 = plist1->next;        }    }    else    {        count = -count;        while (count--)        {            plist2 = plist2->next;        }    }    while (plist1 != plist2)    {        plist1 = plist1->next;        plist2 = plist2->next;    }    return plist1;}

void Test1(){    ListNode *plist1 = NULL;    ListNode *plist2 = NULL;    bool flag = true;if (flag)    {        printf("相交！\n");        printf("交点为：%d\n",AnswerMeetNode(plist1,plist2)->data);    }    else    {        printf("不想交！\n");    }}

2.判断两个链表是否相交，若相交，求交点。（假设可能带环）

1).两个都不带环
有可能相交，有可能不相交

2).一个带环一个不带环，必定不相交。

3).两个都带环
不相交
相交：交点不在环上；交点在环上

//判断两个链表是否相交，若相交，求交点.（假设链表可能带环）CheckNoode CheckIsMeetTop(ListNode *plist1, ListNode *plist2){    ListNode *tmp1 = NULL;    ListNode *tmp2 = NULL;    CheckNoode ret = { 0, NULL, NULL };    tmp1 = IsCycle(plist1);    tmp2 = IsCycle(plist2);    if ((tmp1 == NULL) && (tmp2 == NULL))    {        //都不带环        tmp1 = plist1;        tmp2 = plist2;        while (tmp1->next != NULL)        {            tmp1 = tmp1->next;        }        while (tmp2->next != NULL)        {            tmp2 = tmp2->next;        }        if (tmp1 == tmp2)        {            //相交            ret.plist1 = AnswerMeetNode(plist1, plist2);            ret.flag = 1;            return ret;        }        else        {            //不相交            ret.flag = 1;            return ret;        }    }    else if ((tmp1 != NULL) && (tmp2 != NULL))    {        //两者都带环        ListNode *tmp = tmp1->next;        while ((tmp != tmp2) && (tmp != tmp1))        {            tmp = tmp->next;        }        if (tmp == tmp2)        {            //相交            tmp1 = GetCycleEnter(plist1,tmp1);            tmp2 = GetCycleEnter(plist2,tmp2);            if (tmp1 == tmp2)            {                //交点在链上                int count1 = 0;                int count2 = 0;                int count = 0;                ListNode *cur1 = plist1;                ListNode *cur2 = plist2;                while (cur1 != tmp1)                {                    count1++;                    cur1 = cur1->next;                }                while (cur2 != tmp1)                {                    count2++;                    cur2 = cur2->next;                }                count = count1 - count2;                if (count > 0)                {                    while (count--)                    {                        plist1 = plist1->next;                    }                }                else                {                    count = -count;                    while (count--)                    {                        plist2 = plist2->next;                    }                }                while (plist1 != plist2)                {                    plist1 = plist1->next;                    plist2 = plist2->next;                }                ret.plist1 = plist1;                ret.flag = 3;                return ret;            }            else            {                //两个交点都在环上                ret.plist1 = tmp1;                ret.plist2 = tmp2;                ret.flag = 3;                return ret;            }        }        else        {            //不相交            ret.flag = 3;            return ret;        }    }    else    {        //一个带环，一个不带环。必不相交        ret.flag = 2;        return ret;    }}

参考