给定一个单向链表（长度未知），请设计一个既节省时间又节省空间的算法来找出该链表中的倒数第m个元素。实现这个算法，并为可能出现的特例情况安排好处理措施。“倒数第m个元素”是这样规定的：当m=0时，链表的

给定一个单向链表（长度未知），请设计一个既节省时间又节省空间的算法来找出该链表中的倒数第m个元素。实现这个算法，并为可能出现的特例情况安排好处理措施。“倒数第m个元素”是这样规定的：当m=0时，链表的最后一个元素将被返回：

#include <stdlib.h>

#include <stdio.h>

#include <malloc.h>

struct listElementType

{

int data;

listElementType* next;

};

typedef struct listElementType* m_list;

m_list find_the_mth_element_from_end(m_list u_list,int m)

{

m_list p1 = NULL,p2 = NULL;

p1 = u_list;

for (int i = 0; i < m; i++)

{

if (p1->next)

{

p1 = p1->next;

}

else

{

return NULL;

}

}

p2 = u_list;

while (p1->next)

{

p1 = p1->next;

p2 = p2->next;

}

return p2;

}

m_list createList(const int& u_listLength)

{

int i = 0,a = 0;

m_list head = NULL,p1 = NULL,tail = NULL;

for(i = 1; i <= u_listLength; i++)

{

p1 = (m_list)malloc(sizeof(m_list));

if (p1 != NULL)

{

printf("input the %d th number of list:",i);

scanf("%d",&a);

p1->data = a;

if (head == NULL)

{

head = p1;

tail = p1;

}

else

{

tail->next = p1;

tail = p1;

}

tail->next = NULL;

}

else

{

printf("i:%d,p1 malloc error\n",i);

}

}

return head;

}

void freeList(m_list u_list)

{

m_list head,listTmp;

head = u_list;

while (head != NULL)

{

listTmp = head;

head = head->next;

free(listTmp);

listTmp = NULL;

}

listTmp = NULL;

}

void printList(m_list q)

{

while (q)

{

printf("%d ",q->data);

q = q->next;

}

printf("\n");

}

int main(void)

{

m_list u_list = NULL;

int u_listLength = 0;

int u_dstNodePosition = 0;

printf("input the listLength:");

scanf("%d",&u_listLength);

u_list = createList(u_listLength);

if (u_list != NULL)

{

printList(u_list);

printf("input the dstNodePosition:");

scanf("%d",&u_dstNodePosition);

m_list u_destNode = find_the_mth_element_from_end(u_list,u_dstNodePosition);

if (u_destNode)

{

printf("dstNodeData:%d\n",u_destNode->data);

}

else

{

printf("u_dstNodePosition:%d get no Node\n",u_dstNodePosition);

}

freeList(u_list);

}

else

{

printf("list malloc error\n");

return -1;

}

return 0;

}