C 在链表的开头插入元素 [英] C Insert Element At Beginning of Linked List

问题描述

我用 C 语言编写了一个程序，旨在将结构按升序插入链接列表.

I have written a program in C that is designed to insert structures in an ascending order into a Linked List.

问题在于没有插入我的两个最低值(1 和 2).这是因为我目前没有工作处理程序来检查链表的第一个值是否已经大于给定的值.

The problem is that is is not inserting my two lowest values (1 and 2). This is because I don't currently have a working handler to check if the first value of the linked list is already greater than the given.

这是我的功能:

struct PCB
{
    struct PCB *Next_PCB ;
    int PID ;
};

void insert_ordered (struct PCB *Head, struct PCB *Add)
{
    tmp = Head;
    if (Head->PID == 0) {
        Head->PID = Add->PID;
    } else {
        if (Head->Next_PCB == NULL) {
            Head->Next_PCB = Add;
        } else {
            int count = 0;
            while (Head != NULL) {
                if (Add->PID > Head->PID) {
                    if (Head->Next_PCB != NULL) {
                        Head = Head->Next_PCB;
                        count++;
                    } else {
                        Head->Next_PCB = Add;
                        break;
                    }
                } else if (Add->PID == Head->PID) {
                    Add->Next_PCB = Head->Next_PCB;
                    Head->Next_PCB = Add;
                    break;
                } else if (Add->PID < Head->PID) {
                    if (Add->PID == 1 || Add->PID == 2) {
                        printf("found 1 or 2");
                        printf("count: %d", count);
                    }
                    int ct = 0;
                    while (tmp != NULL) {
                        if (count == 0) {
                            printf("made it, %d", ct);
                            Add->Next_PCB = tmp;
                            break;
                        } else if (ct == (count - 1)) {
                            Add->Next_PCB = Head;
                            tmp->Next_PCB = Add;
                            break;
                        }
                        tmp = tmp->Next_PCB;
                        ct++;
                    }
                    break;
                }
            }
        }
    }
    printf("pid : %d
", Add->PID);
}

这是我打印出列表后的输出:

Here is my output after printing out the list:

pid : 6
pid : 17
pid : 15
pid : 13
pid : 15
pid : 6
pid : 12
pid : 9
found 1 or 2count: 0made it, 0pid : 1
found 1 or 2count: 0made it, 0pid : 2
pid : 7
pid : 10
pid : 19

-------------------
PID: 6
PID: 6
PID: 7
PID: 9
PID: 10
PID: 12
PID: 13
PID: 15
PID: 15
PID: 17
PID: 19

输出应该在两个 6 之前有一个 1 和一个 2.有人可以帮帮我吗?谢谢.

The output SHOULD have a 1 and a 2 before the two sixes. Can anybody help me out? Thanks.

推荐答案

void insert_ordered (struct PCB *Head, struct PCB *Add) : 无法替换元素的头部这个界面.所以，你需要把第一个元素中的dummy元素(Anchor node即不是预期的内容持有).
下面是一个具体的例子:

void insert_ordered (struct PCB *Head, struct PCB *Add) : It is not possible to replace the head of the elements in this interface. So, you need to the first element in the dummy elements(Anchor node that is not intended contents of the holding).
The following is a specific example:

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

struct PCB{
    struct PCB *Next_PCB ;
    int PID ;
};

struct PCB *new_PCB(int PID){
    struct PCB *pcb = malloc(sizeof(*pcb));
    if(pcb != NULL){
        pcb->Next_PCB = NULL;
        pcb->PID = PID;
    }
    return pcb;
}

void insert_ordered (struct PCB *Head, struct PCB *Add){
    if(Head == NULL)
        return ;//can't

    struct PCB *prev = Head, *curr = Head->Next_PCB;
/*  this is reduced to following while-loop
    if(Head->Next_PCB == NULL){//empty list
        Head->Next_PCB = Add;
        return ;
    }
    if(Add->PID <= curr-> PID){//Add node <= Top node
        prev->Next_PCB = Add;
        Add->Next_PCB = curr;
        return ;
    }
*/
    while(curr != NULL && curr->PID < Add->PID){
        prev = curr;
        curr = curr->Next_PCB;
    }
    prev->Next_PCB = Add;
    Add->Next_PCB = curr;
}

void print(struct PCB *Head){
    if(Head == NULL)
        return ;
    else
        Head = Head->Next_PCB;
    while(Head != NULL){
        printf("PID: %d
", Head->PID);
        Head = Head->Next_PCB;
    }
}

//alias
#define Make_list() new_PCB(-1)

int main(void){
    struct PCB *head = Make_list();
    //struct PCB *head = new_PCB(-1);//dummy node, This is intended to holds a list.
    insert_ordered (head, new_PCB( 6));
    insert_ordered (head, new_PCB(17));
    insert_ordered (head, new_PCB(15));
    insert_ordered (head, new_PCB(13));
    insert_ordered (head, new_PCB(15));
    insert_ordered (head, new_PCB( 6));
    insert_ordered (head, new_PCB(12));
    insert_ordered (head, new_PCB( 9));
    insert_ordered (head, new_PCB( 1));
    insert_ordered (head, new_PCB( 2));
    insert_ordered (head, new_PCB( 7));
    insert_ordered (head, new_PCB(10));
    insert_ordered (head, new_PCB(19));

    print(head);
    //release list
    return 0;
}

或者你需要像排序一样交换内容.

Or you need to swap the contents like a sort.

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