链表常见面试题

http://blog.csdn.net/lxgwm2008/article/details/8907930
一、头文件

#ifndef LISTUTILS_H
#define LISTUTILS_H

typedef int ElemType;

typedef struct _node
{
    ElemType data;
    struct _node *next;
} Node;

/*
Description: get the intersection point of two list
Param:       headA: header of list1
             headB: header of list2
Return:      the intersection point or null for none
*/
const Node *GetIntersectionPoint(const Node *headA, const Node *headB);

/*
Description: reverse the given list
Param:       head: header of list
Return:      none
*/
void ReverseList(Node *head);

/*
Description: get the circle point of list
Param:       head: header of list
Return:      the circle point or null for none
*/
const Node *GetCirclePoint(const Node *head);

void PrintList(Node *head);
#endif // LISTUTILS_H

二、C文件

#include
#include "ListUtils.h"

const Node *GetIntersectionPoint(const Node *headA, const Node *headB)
{
    const Node *tmpA, *tmpB;
    unsigned int lenA = 0, lenB = 0, i;

    if(NULL == headA || NULL == headB || NULL == headA->next || NULL == headB->next){
        return NULL;
    }

    tmpA = headA;
    //make tmpA points to the end of headA
    while(NULL != tmpA->next){
        tmpA = tmpA->next;
        ++lenA;
    }

    tmpB = headB;
    //make tmpB points to the end of headB
    while(NULL != tmpB->next){
        tmpB = tmpB->next;
        ++lenB;
    }

    //no intersection point
    if(tmpA != tmpB){
        return NULL;
    }

    tmpA = headA->next;
    tmpB = headB->next;
    if(lenA > lenB){
        for(i = 0; i < lenA - lenB; ++i){
            tmpA = tmpA->next;
        }
    }else if(lenB > lenA){
        for(i = 0; i < lenB - lenA; ++i){
            tmpB = tmpB->next;
        }
    }

    while(tmpA != tmpB){
        tmpA = tmpA->next;
        tmpB = tmpB->next;
    }

    return tmpA;
}

const Node *GetCirclePoint(const Node *head)
{
    Node *fast = NULL;
    Node *slow = NULL;
    Node *circlePoint  = NULL;

    //empty list
    if(NULL == head || NULL == head->next){
        return NULL;
    }

    fast = slow = head->next;
    while(fast && fast->next){
        fast = fast->next->next;
        slow = slow->next;
        if(fast == slow){
            circlePoint = fast;
            break;
        }
    }

    //no circlePoint
    if(NULL == circlePoint){
        return NULL;
    }

    fast = head->next;
    while(fast != slow){
        fast = fast->next;
        slow = slow->next;
    }

    return fast;
}

void ReverseList(Node *head)
{
    Node *first, *second, *third;

    //if there is less than one node, return
    if(NULL == head || NULL == head->next){
        return;
    }

    first = head->next;
    second = first->next;
    first->next = NULL;
    while(second){
        //cache the next node of "second"
        third = second->next;
        //insert the "second" node to the front of result list
        second->next = first;
        //move the first node to point to "second"
        first = second;
        //restore the "second" node
        second = third;
    }

    head->next = first;

    return;
}

void PrintList(Node *head)
{
    Node *node;
    int pos = -1;
    if(NULL == head)
    {
        return;
    }
    node = head->next;
    while(node)
    {
        printf("[%d]----[%d]\n", ++pos, node->data);
        node = node->next;
    }
}