c - 拆分链表

Question

为什么这个程序中的拆分列表总是空的？ (它源自链接列表上 Wikipedia 页面上的代码。)

/* 
    Example program from wikipedia linked list article
    Modified to find nth node and to split the list
*/

#include <stdio.h>
#include <stdlib.h>

typedef struct ns
{
    int data;
    struct ns *next; /* pointer to next element in list */
} node;

node *list_add(node **p, int i)
{
    node *n = (node *)malloc(sizeof(node));
    if (n == NULL)
        return NULL;

    n->next = *p; //* the previous element (*p) now becomes the "next" element */
    *p = n;       //* add new empty element to the front (head) of the list */
    n->data = i;

    return *p;
}

void list_print(node *n)
{
    int i=0;
    if (n == NULL)
    {
        printf("list is empty\n");
    }
    while (n != NULL)
    {
        printf("Value at node #%d = %d\n", i, n->data);
        n = n->next;
        i++;
    }
}

node *list_nth(node *head, int index) {
    node *current = head;
    node *temp=NULL;
    int count = 0; // the index of the node we're currently looking at
    while (current != NULL) {
        if (count == index)
            temp = current;
        count++;
        current = current->next;
    }
    return temp;
}
/* 
This function is to split a linked list:
Return a list with nodes starting from index 'int ind' and
step the index by 'int step' until the end of list.
*/
node *list_split(node *head, int ind, int step) {
    node *current = head;
    node *temp=NULL;
    int count = ind; // the index of the node we're currently looking at
    temp = list_nth(current, ind);
    while (current != NULL) {
        count = count+step;
        temp->next = list_nth(head, count);
        current = current->next;
    }

    return temp; /* return the final stepped list */
}

int main(void)
{
    node *n = NULL, *list1=NULL, *list2=NULL, *list3=NULL, *list4=NULL;
    int i;
    /* List with 30 nodes */
    for(i=0;i<=30;i++){
        list_add(&n, i);
    }
    list_print(n);

    /* Get 1th, 5th, 9th, 13th, 18th ... nodes of n etc */ 

    list1 = list_split(n, 1, 4);

    list_print(list1);

    list2 = list_split(n, 2, 4); /* 2, 6, 10, 14 etc */   
    list_print(list2);

    list3 = list_split(n, 3, 4); /* 3, 7, 11, 15 etc */   
    list_print(list3);

    list3 = list_split(n, 4, 4); /* 4, 8, 12, 16 etc */   
    list_print(list4);

    getch();
    return 0;
}

Answer 1

 temp = list_nth(current, ind);

 while (current != NULL) {
        count = count+step;
        temp->next = list_nth(head, count);
        current = current->next;
    }

您找到了开始拆分的正确项目，但是看看从那时起 temp 发生了什么……您只分配给 temp->next。

您需要跟踪拆分列表的头部和插入新项目的尾部。