I have a problem with swap code in Doubly linked list
Question
I made swap code in C but I didn't get perfect grade in school compiler. I think there is a problem with following code. I made doubly linked list with struct and pointer. Node is defined that:
struct node* newnode(char x)
{
struct node* new = (struct node*)malloc(sizeof(struct node));
new->next = NULL;
new->prev = NULL;
new->c = x;
return new;
}
And the following code is swap code that I made each function factor mean that "struct node*p" is full list from head to tail, "int a and b" is rank of list and "count1(p)" is function that count node in full list and return number of node (exclude head and tail).
void swap(struct node* p, int a, int b)
{
int x, y;
struct node* x1, * x2, emp = { 0 };
int i = 0;
x1 = p;
x2 = p;
if (a >= b) {
x = b;
y = a;
}
else {
x = a;
y = b;
}
if (b <= 0 || a <= 0 || a > N || a > count1(p) || b > N || b > count1(p)) {
printf("invalid position\n");
return;
}while (i < x && x1 != tail) {
x1 = x1->next;
i++;
}
i = 0;
while (i < y && p != tail) {
x2 = x2->next;
i++;
}
if (x1->next != x2)
{
x1->prev->next = x2;
x1->next->prev = x2;
x2->prev->next = x1;
x2->next->prev = x1;
emp.next = x1->next;
emp.prev = x1->prev;
x1->next = x2->next;
x1->prev = x2->prev;
x2->next = emp.next;
x2->prev = emp.prev;
}
if (x1->next == x2)
{
emp.prev = x1->prev;
emp.next = x1->next;
x1->prev->next = x2;
x2->next->prev = x1;
x1->prev = x2;
x1->next = x2->next;
x2->prev = emp.prev;
x2->next = x1;
}
}
The following code is my full code:
#include<stdio.h>
#include<stdlib.h>
int N;
struct node {
struct node* next;
struct node* prev;
char c;
};
struct node* head, * tail;
void reset() {
head = (struct node*)malloc(sizeof(struct node));
tail = (struct node*)malloc(sizeof(struct node));
head->prev = NULL;
head->next = tail;
head->c = NULL;
tail->prev = head;
tail->next = NULL;
tail->c = NULL;
}
struct node* newnode(char x)
{
struct node* new = (struct node*)malloc(sizeof(struct node));
new->next = NULL;
new->prev = NULL;
new->c = x;
return new;
}
void prcount(struct node* p)
{
printf("%d\n", count1(p));
}
int count1(struct node* p)
{
int sum = 0;
while (p != tail) {
p = p->next;
sum++;
}
return sum + -1;
}
void add1(struct node* p, int n, char x)
{
struct node* new1 = newnode(x);
int i = 1;
if (n <= 0 || n > N || n > count1(p) + 1) {
printf("invalid position\n");
return;
}
while (i < n && p != tail) {
p = p->next;
i++;
}
p->next->prev = new1;
new1->prev = p;
new1->next = p->next;
p->next = new1;
}
void delete1(struct node* p, int n)
{
int i = 0;
if (n <= 0 || n > N || n > count1(p)) {
printf("invalid position\n");
return;
}
while (i < n && p != tail)
{
p = p->next;
i++;
}
p->prev->next = p->next;
p->next->prev = p->prev;
free(p);
}
void get1(struct node* p, int n) {
int i = 0;
if (n <= 0 || n > N || n > count1(p)) {
printf("invalid position\n");
return;
}while (i < n && p != tail) {
p = p->next;
i++;
}
printf("%c\n", p->c);
}
void print1(struct node* p)
{
int i = 0;
if (count1(p) == 0) {
printf("invalid position\n");
return;
}
while (i < N && p->next != tail)
{
p = p->next;
printf("%c", p->c);
i++;
}
printf("\n");
}void removeall(struct node* p)
{
struct node* emp;
p = p->next;
while (p != tail)
{
emp = p->next;
free(p);
p = emp;
}
head->prev = NULL;
head->next = tail;
head->c = NULL;
tail->prev = head;
tail->next = NULL;
tail->c = NULL;
}
void swap(struct node* p, int a, int b)
{
int x, y;
struct node* x1, * x2, emp = { 0 };
int i = 0;
x1 = p;
x2 = p;
if (a >= b) {
x = b;
y = a;
}
else {
x = a;
y = b;
}
if (b <= 0 || a <= 0 || a > N || a > count1(p) || b > N || b > count1(p)) {
printf("invalid position\n");
return;
}while (i < x && x1 != tail) {
x1 = x1->next;
i++;
}
i = 0;
while (i < y && x2 != tail) {
x2 = x2->next;
i++;
}
if (x1->next != x2)
{
x1->prev->next = x2;
x1->next->prev = x2;
x2->prev->next = x1;
x2->next->prev = x1;
emp.next = x1->next;
emp.prev = x1->prev;
x1->next = x2->next;
x1->prev = x2->prev;
x2->next = emp.next;
x2->prev = emp.prev;
}
if (x1->next == x2)
{
emp.prev = x1->prev;
emp.next = x1->next;
x1->prev->next = x2;
x2->next->prev = x1;
x1->prev = x2;
x1->next = x2->next;
x2->prev = emp.prev;
x2->next = x1;
}
}
int main()
{
int i;
int r, n;
char x, y;
reset();
scanf("%d", &N);
for (i = 0; i < N; i++)
{
scanf(" %c", &x);
if (x == 'A') {//A mean add(head,int a, char x) -> add 'x' on a rank in list
scanf("%d", &r);
scanf(" %c", &y);
add1(head, r, y);
}
else if (x == 'D') {// D mean delete(struct node *head, int a) -> delete element on int a rank
scanf("%d", &r);
delete1(head, r);
}
else if (x == 'G') {//G mean Get(head,int a)-> print element on int a rank
scanf("%d", &r);
get1(head, r);
}
else if (x == 'P') {//P mean print(head) -> print all element in list
print1(head);
}
else if (x == 'R') {//R mean Removeall(head) -> remove all node (exclude head and tail0
removeall(head);
}
else if (x == 'C')//C Mean prcount(head) -> count and print number of node in list (exclude head and tail)
{
prcount(head);
}
else if (x == 'S') {//S mean Swap(head, int a, int b) -> swap element of int a rank with int b rank
scanf("%d", &r);
scanf("%d", &n);
swap(head, r, n);
}
}
removeall(head);
}
It's my full code. I want to know is there any problem Or more effective way to make swap code?
2 answers
solution1
0 2021-04-02 11:18:58
#include<stdio.h>
#include<stdlib.h>
int N;
struct node {
struct node* next;
struct node* prev;
char c;
};
struct node* head, * tail;
void reset() {
head = (struct node*)malloc(sizeof(struct node));
tail = (struct node*)malloc(sizeof(struct node));
head->prev = NULL;
head->next = tail;
head->c = NULL;
tail->prev = head;
tail->next = NULL;
tail->c = NULL;
}
struct node* newnode(char x)
{
struct node* new = (struct node*)malloc(sizeof(struct node));
new->next = NULL;
new->prev = NULL;
new->c = x;
return new;
}
void prcount(struct node* p)
{
printf("%d\n", count1(p));
}
int count1(struct node* p)
{
int sum = 0;
while (p != tail) {
p = p->next;
sum++;
}
return sum + -1;
}
void add1(struct node* p, int n, char x)
{
struct node * new1 = newnode(x);
int i = 1;
if (n<=0||n > N || n > count1(p) + 1) {
printf("invalid position\n");
return;
}
while (i < n && p != tail) {
p = p->next;
i++;
}
p->next->prev = new1;
new1->prev = p;
new1->next = p->next;
p->next = new1;
}
void delete1(struct node* p, int n)
{
int i = 0;
if (n <= 0 || n > N || n > count1(p)) {
printf("invalid position\n");
return;
}
while (i < n && p != tail)
{
p = p->next;
i++;
}
p->prev->next = p->next;
p->next->prev = p->prev;
free(p);
}
void get1(struct node* p, int n) {
int i = 0;
if (n <= 0 || n > N || n > count1(p)) {
printf("invalid position\n");
return;
}while (i < n && p != tail) {
p = p->next;
i++;
}
printf("%c\n", p->c);
}
void print1(struct node* p)
{
int i = 0;
if (count1(p) == 0) {
printf("invalid position\n");
return;
}
while (i < N && p->next != tail)
{
p = p->next;
printf("%c", p->c);
i++;
}
printf("\n");
}void removeall(struct node* p)
{
struct node* emp;
p = p->next;
while (p != tail)
{
emp = p->next;
free(p);
p = emp;
}
head->prev = NULL;
head->next = tail;
head->c = NULL;
tail->prev = head;
tail->next = NULL;
tail->c = NULL;
}
void swap(struct node* p, int a, int b)
{
int x, y;
struct node* x1, * x2, emp = { 0 };
int i = 0;
x1 = p;
x2 = p;
if (a >= b) {
x = b;
y = a;
}
else {
x = a;
y = b;
}
if (b <= 0 || a <= 0 || a > N || a > count1(p) || b > N || b > count1(p)) {
printf("invalid position\n");
return;
}while (i < x && x1 != tail) {
x1 = x1->next;
i++;
}
i = 0;
while (i < y && p != tail) {
x2 = x2->next;
i++;
}
if (x1->next != x2)
{
x1->prev->next = x2;
x1->next->prev = x2;
x2->prev->next = x1;
x2->next->prev = x1;
emp.next = x1->next;
emp.prev = x1->prev;
x1->next = x2->next;
x1->prev = x2->prev;
x2->next = emp.next;
x2->prev = emp.prev;
}
if (x1->next == x2)
{
emp.prev = x1->prev;
emp.next = x1->next;
x1->prev->next = x2;
x2->next->prev = x1;
x1->prev = x2;
x1->next = x2->next;
x2->prev = emp.prev;
x2->next = x1;
}
}
int main()
{
int i;
int r, n;
char x, y;
reset();
scanf("%d", &N);
for (i = 0; i < N; i++)
{
scanf(" %c", &x);
if (x == 'A') {
scanf("%d", &r);
scanf(" %c", &y);
add1(head, r, y);
}
else if (x == 'D') {
scanf("%d", &r);
delete1(head, r);
}
else if (x == 'G') {
scanf("%d", &r);
get1(head, r);
}
else if (x == 'P') {
print1(head);
}
else if (x == 'R') {
removeall(head);
}
else if (x == 'C')
{
prcount(head);
}
else if (x == 'S') {
scanf("%d", &r);
scanf("%d", &n);
swap(head, r, n);
}
}
removeall(head);
}
it is my full code
solution2
0 2021-04-02 12:06:55
int N is used as the number of input commands in main . The comparisons with N in your list functions (as if N would denote the number of nodes) make no sense - you could just drop them.
Besides that, there are some places where a compiler with appropriate options would issue warnings - perhaps that's why you didnt get perfect grade in school compiler .
head->c = NULL;
Since c is of type char and NULL is a null pointer constant this doesn't fit; change to
head->c = '\0'; // or head->c = 0;
printf("%d\n", count1(p));
There you call count1 before it is declared. Declare it before use with
int count1(struct node* p);
or move the function definition before the first function using it.
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