链表插入排序，有错！该如何解决

2012-08-01

链表插入排序，有错！C/C++ code#includestdio.h#includestdlib.htypedef struct node *linkstruct nod

链表插入排序，有错！

C/C++ code

#include<stdio.h>#include<stdlib.h>typedef struct node *link;struct node {    int item;    link next;};link InsertSort(link head);int main(){    int i;    int N;    link heada,x,y;    while (scanf("%d", &N) == 1)    {        heada = (struct node *)malloc (sizeof(struct node));        x = heada;        heada->next = NULL;        //构造链表        for (i = 1; i <= N; i++)        {            x = (x->next = (struct node *)malloc(sizeof(struct node)));            x->item = rand()%1000;            x->next = NULL;        }        //插入排序        y = InsertSort(heada);        while (y)        {            printf("%-4d", y->item);            y = y->next;        }    }    return 0;}//插入排序函数link InsertSort(link heada){    link headb,a,b,t,u,x;    headb = (struct node *)malloc (sizeof(struct node));    a = heada;    b = headb;    b->next = NULL;            for (t = a->next; t != NULL; t = u)    {        u = t->next;        for (x = b; x != NULL; x = x->next)        {            if (x->next->item > t->item)//断点后这里有错                                            break;        }        t->next = x->next;        x->next = t;    }    return headb;}

有错，程序有错！请各位指教指教！

[解决办法]
错误引起的原因如下:

C/C++ code

#include<stdio.h>#include<stdlib.h>typedef struct node *link;struct node {    int item;    link next;};link InsertSort(link head);int main(){    int i;    int N;    link heada,x,y;    while (scanf("%d", &N) == 1)    {        heada = (struct node *)malloc (sizeof(struct node));        x = heada;        heada->next = NULL;        //构造链表        for (i = 1; i <= N; i++)        {            x = (x->next = (struct node *)malloc(sizeof(struct node)));            x->item = rand()%1000;            x->next = NULL;        }        //插入排序        y = InsertSort(heada);        while (y)        {            printf("%-4d", y->item);            y = y->next;        }    }    return 0;}//插入排序函数link InsertSort(link heada){    link headb,a,b,t,u,x;    headb = (struct node *)malloc (sizeof(struct node));    a = heada;    b = headb;    b->next = NULL;//b的next为NULL    for (t = a->next; t != NULL; t = u)    {        u = t->next;        for (x = b; x != NULL; x = x->next)        {            if (x->next->item > t->item)//断点后这里有错---->b的next为NULL x初值为b b->next为 NULL，对NULL取->item自然要出错                                break;        }        t->next = x->next;        x->next = t;    }    return headb;}
[解决办法]
C/C++ code#include<stdio.h>#include<stdlib.h>typedef struct node {    int item;    struct node* next;}*link;link InsertSort(link head);int main(){    int i;    int N;    link heada,x,y;//    srand(time(0));    while (scanf("%d", &N) == 1)    {        heada = (struct node *)malloc (sizeof(struct node));        x = heada;        heada->next = NULL;        //构造链表        for (i = 1; i <= N; i++)        {            x = (x->next = (struct node *)malloc(sizeof(struct node)));            x->item = rand()%1000;            x->next = NULL;        }        //插入排序        y = InsertSort(heada);        y = y->next;        while (y)        {            printf("%-4d", y->item);            y = y->next;        }    }    return 0;}//插入排序函数link InsertSort(link heada){    link headb,a,b,t,u,x;    headb = (struct node *)malloc (sizeof(struct node));    a = heada;    b = headb;    b->next = NULL;    for (t = a->next; t != NULL; t = u)    {        u = t->next;        for (x = b; x != NULL; x = x->next)        {            if (x->next==NULL || x->next->item > t->item)//断点后这里有错                                break;        }        t->next = x->next;        x->next = t;    }    return headb;}

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链表插入排序，有错！该如何解决