单链表相关问题

/*
判断单链表是否存在环

1）暴力：双层循环遍历（n^2）
2）双指针：快指针fast=NULL,慢指针slow=NULL
int judge(link head)
{
    if(NULL==head) return false;
    link fast = head,
         slow = head;
    while(slow!=NULL && fast!=NULL)
    {
        slow = slow->next;
        fast = fast->next->next;
        if(slow==fast)
        {
            return true;
        }
    }
    return false;
}

计算带环单链表的长度

int count(link head)
{
    if(NULL==head)
        return false;
    link fast = head,
         slow = head;
    while(slow!=NULL && fast!=NULL)
    {
        slow = slow->next;
        fast = fast->next->next;
        if(slow==fast)
        {
            flag = true;
            break;
        }
    }
    if(flag)
    {
        int ans = 1;
        slow = slow->next;
        while(slow!=fast)
        {
            ans++;
            slow = slow->next;
        }
        return ans ;
    }
    return false;
}

查找单链表中环的入口

设环长为n，非环形部分长度为m
link find(link head)
{
    int flag = false;
    if(NULL==head) return false;
    link fast = head,
         slow = head;
    while(slow!=NULL && fast!=NULL)
    {
        slow = slow->next;
        fast = fast->next->next;
        if(slow==fast)
        {
            flag=true;
            break;
        }
    }
    if(flag)
    {
        slow = head;
        while(slow!=fast)
        {
            slow = slow->next;
            fast = fast->next;
        }
        return slow;
    }
    return NULL;
}