问题描述
我了解如何在O（v + e）中创建邻接表。现在，我的实现扫描边缘，然后将其推入各个顶点的邻接列表。例如，输入为：
1 2
3 6
4 2
1 6
5 3
输出将是
1: 2,6
2: 1,4
3: 5,6
4: 2
5: 3
6: 1,3
边缘以任意顺序给出。
每个节点都有一个列表。我希望列表按升序排列。我坚信没有办法在固定时间内按升序推入邻接表。我错了吗？
这是我的代码：
#include <stdio.h>
#include <stdlib.h>
// created linked list and Node structures
typedef struct node{
int vertexnumber;
struct node* next;
} Node;
typedef struct linkedList{
Node* head;
int size;
} LinkedList;
void getNumberOfVerticesAndEdges(FILE* fp,int* vertices,int* edges);
void push(LinkedList* linkedList,int vertex);
Node* createNode(int vertexnumber);
void printAdjacencyLists(LinkedList** arrayOfLinkedLists,int vertices,int edges);
LinkedList** createLinkedList(int numOfVertices);
void formatList(LinkedList** array,int vertices);
int main(void){
// creating the file pointer
FILE *fptr = fopen("input-machine-problem-1.txt","r");
if (fptr == NULL) {
printf("Error! opening file");
return 0;
}
int edges;
int vertices;
int* edgesPtr = &edges;
int* verticesPtr = &vertices;
// gets the number of vertices and edges in the file
getNumberOfVerticesAndEdges(fptr,verticesPtr,edgesPtr); // O(e)
// creating an array of linked lists,each list stores adjacency list for a vertex
LinkedList** arrayOfLinkedLists = createLinkedList(vertices);
int x,y;
if(fptr == NULL){
return 0;
}
// rewind so that any outside functions (getNumberOfVerticesAndEdges for example) reading file do not move
// the pointer to a spot that will affect the algorithm belowe
rewind(fptr);
// looping for every vertice,scan and push each edge causing O(v * e) time complexity
for(int i = 0; i < edges; i++){
// read each edge from the file
if(feof(fptr)){
return 0;
}
fscanf (fptr,"%d %d",&x,&y);
push(arrayOfLinkedLists[x - 1],y);
push(arrayOfLinkedLists[y - 1],x);
}
// implementation makes use of setting a temp node to each linked list initialized so funciton below removes that temp node
formatList(arrayOfLinkedLists,vertices);
// prints adjacency lists in readable format
printAdjacencyLists(arrayOfLinkedLists,vertices,edges);
// closes file
fclose(fptr);
}
// O(v)
// input array of LinkedLists,and int value for a new nodes vertex that is being pushed
void push(LinkedList* linkedList,int vertex){
// creates new node with input int
Node* newNode = createNode(vertex);
// functionality below creates a pointer that will traverse the linked list,moving the new node over 1 position
// until it finds a node that is greater than the new node,so new node will be node right before the first
// one greater than it
Node temp;
Node* cur = &temp;
temp.next = linkedList->head;
while(cur->next != NULL && cur->next->vertexnumber < newNode->vertexnumber){
cur = cur->next;
}
if(cur->next->vertexnumber == newNode->vertexnumber){
return;
}
newNode->next = cur->next;
cur->next = newNode;
linkedList->head = temp.next;
}
// removes place holder node
void formatList(LinkedList** array,int vertices){
for(int i = 0;i < vertices; i++){
Node* temp = array[i]->head;
Node* prev = temp;
while(temp->next != NULL){
prev = temp;
temp = temp->next;
}
prev->next = NULL;
}
}
// creates array of linked lists and initializes each list with a temp/place holder node
LinkedList** createLinkedList(int numOfVertices){
LinkedList** array = malloc(sizeof(LinkedList) * numOfVertices);
for(int i = 0; i < numOfVertices; i++){
LinkedList* newLinkedList = malloc(sizeof(LinkedList));
Node* temp = createNode(99);
newLinkedList->head = temp;
array[i] = newLinkedList;
}
return array;
}
// allocates memory for a node and sets its vetex int value
Node* createNode(int vertexnumber){
Node* newNode = malloc(sizeof(Node));
if(!newNode){
return NULL;
}
newNode->vertexnumber = 0;
newNode->next = NULL;
newNode->vertexnumber = vertexnumber;
return newNode;
}
// scans through file and looks for greatest int and increments int holding num of edges for every new line of ints read
void getNumberOfVerticesAndEdges(FILE* fp,int* edges){
int x,y;
if (fp == NULL) {
printf("Error! opening file");
return;
}
*vertices = 0;
*edges = 0;
while (fscanf(fp,&y) == 2) {
if(x > *vertices){
*vertices = x;
} if (y > *vertices){
*vertices = y;
}
*edges = (*edges) + 1;
}
}
// traverses each linked list and prints its vertices value
void printAdjacencyLists(LinkedList** arrayOfLinkedLists,int edges){
for(int i = 0; i < vertices; i++){
printf("%d: ",i + 1);
if(arrayOfLinkedLists[i]->head == NULL){
return;
}
Node* cur = arrayOfLinkedLists[i]->head;
while(cur != NULL){
printf("%d --> ",cur->vertexnumber);
cur = cur->next;
}
printf("NULL\n");
free(cur);
}
}
唯一相关的部分是main和我的push方法中的for循环，因为它们是影响复杂性的两个因素
解决方法
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