การแทรกและการลบ

การแก้ไขรายการ

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

int main(void) {
    struct Node *head = make(2);
    printf("start: %d\n", head->value);
    free(head);
    return 0;
}

แทรกที่ด้านหน้า

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

int main(void) {
    struct Node *head = make(2);
    struct Node *fresh = make(1);
    fresh->next = head;
    head = fresh;
    printf("%d -> %d\n", head->value, head->next->value);
    return 0;
}

เหตุผลที่ต้องส่งตัวชี้ซ้อน

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

void push(struct Node **head, int v) {
    struct Node *n = make(v);
    n->next = *head;
    *head = n;
}

int main(void) {
    struct Node *head = NULL;
    push(&head, 5);
    push(&head, 4);
    printf("%d %d\n", head->value, head->next->value);
    return 0;
}

แทรกที่ด้านท้าย

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

void append(struct Node **head, int v) {
    struct Node *n = make(v);
    if (!*head) { *head = n; return; }
    struct Node *p = *head;
    while (p->next) p = p->next;
    p->next = n;
}

int main(void) {
    struct Node *head = NULL;
    append(&head, 1); append(&head, 2);
    printf("%d %d\n", head->value, head->next->value);
    return 0;
}

แทรกหลังโหนด

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

void insert_after(struct Node *node, int v) {
    struct Node *n = make(v);
    n->next = node->next;
    node->next = n;
}

int main(void) {
    struct Node *head = make(1);
    head->next = make(3);
    insert_after(head, 2);
    printf("%d %d %d\n", head->value, head->next->value, head->next->next->value);
    return 0;
}

ลำดับการทำงานมีความสำคัญ

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

int main(void) {
    struct Node *a = make(1), *c = make(3);
    a->next = c;
    struct Node *b = make(2);
    b->next = a->next;
    a->next = b;
    printf("%d %d %d\n", a->value, b->value, c->value);
    return 0;
}

ลบโหนดแรก

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

void pop(struct Node **head) {
    if (!*head) return;
    struct Node *old = *head;
    *head = old->next;
    free(old);
}

int main(void) {
    struct Node *head = make(1);
    head->next = make(2);
    pop(&head);
    printf("new head: %d\n", head->value);
    free(head);
    return 0;
}

ลบตามค่า

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

void del(struct Node **head, int v) {
    struct Node *cur = *head, *prev = NULL;
    while (cur && cur->value != v) { prev = cur; cur = cur->next; }
    if (!cur) return;
    if (prev) prev->next = cur->next; else *head = cur->next;
    free(cur);
}

int main(void) {
    struct Node *head = make(1);
    head->next = make(2);
    head->next->next = make(3);
    del(&head, 2);
    printf("%d %d\n", head->value, head->next->value);
    return 0;
}

จัดการกรณีหัวรายการ

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

int main(void) {
    struct Node *head = make(1);
    head->next = make(2);
    struct Node *old = head;
    head = head->next;
    free(old);
    printf("head now %d\n", head->value);
    free(head);
    return 0;
}

ป้องกันหน่วยความจำรั่ว

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

int main(void) {
    struct Node *n = make(7);
    free(n);
    printf("node freed, no leak\n");
    return 0;
}

การแทรกโดยคงลำดับไว้เป็นทางเลือก

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

struct Node { int value; struct Node *next; };
struct Node *make(int v){struct Node*n=malloc(sizeof*n);n->value=v;n->next=NULL;return n;}

void insert_sorted(struct Node **head, int v) {
    struct Node *n = make(v);
    if (!*head || (*head)->value >= v) { n->next = *head; *head = n; return; }
    struct Node *p = *head;
    while (p->next && p->next->value < v) p = p->next;
    n->next = p->next; p->next = n;
}

int main(void) {
    struct Node *head = NULL;
    insert_sorted(&head, 3);
    insert_sorted(&head, 1);
    insert_sorted(&head, 2);
    for (struct Node *p = head; p; p = p->next) printf("%d ", p->value);
    printf("\n");
    return 0;
}

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