BFS（邻接表表示）

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

#define VERTEX_NUM 8

typedef enum {FALSE = 0, TRUE = 1}BOOL;

typedef struct ArcNode {
int adjvex;
struct ArcNode *nextarc;    // struct不能少
}ArcNode;

BOOL visited[VERTEX_NUM + 1];    // 访问标志数组（备忘表）

int FirstAdjVex(ArcNode *G[VERTEX_NUM + 1], int v)
{
if (G[v] == NULL)            // v是孤立顶点
return -1;
return G[v]->adjvex;
}

int NextAdjVex(ArcNode *G[VERTEX_NUM + 1], int v, int w)
{
ArcNode *p = NULL;
for (p = G[v]; p != NULL; p = p->nextarc) {
if (p->adjvex == w) {                // 找到w，将返回
if (p->nextarc == NULL)            // w已是v的最后一个邻接点
return -1;
return p->nextarc->adjvex;
}
}
printf("错误！没找到w\n");
return -1;
}

typedef struct Queue {
int arr[VERTEX_NUM + 5];
int front;
int tail;
}Queue;

void BFSTraverse(ArcNode *G[VERTEX_NUM + 1])
{
// 按广度优先非递归遍历图G。使用辅助队列p和访问标志数组visited。
int v;
int w;
int u;
Queue Q;    // 队列长度为VERTEX_NUM，不会假溢出
Q.front = 0;
Q.tail = 0;
for (v = 1; v <= VERTEX_NUM; ++v)
visited[v] = FALSE;

for (v = 1; v <= VERTEX_NUM; ++v) {
if (!visited[v]) {                        // v尚未访问
visited[v] = TRUE;
printf("%d\n", v);
Q.arr[Q.tail++] = v;                // v入队列
while (Q.tail != Q.front) {
u = Q.arr[Q.front++];            // 队头元素出队并置为u
for (w = FirstAdjVex(G, u); w >= 0; w = NextAdjVex(G, u, w)) {
if (!visited[w]) {            // u的尚未访问的邻接顶点w入队列Q
visited[w] = TRUE;
printf("%d\n", w);
Q.arr[Q.tail++] = w;    // w入队列
}
}
}
}
}
}

void CreatAdjListGraph(ArcNode *G[VERTEX_NUM + 1])
{
int a;
int b;
ArcNode *p;
while (scanf("%d %d", &a, &b), !(a == 0 && b == 0)) {    //以0 0作为输入结束
p = (ArcNode *)malloc(sizeof(ArcNode));
if (p == NULL) {
printf("OVERFLOW!\n");
exit(-1);
}
p->adjvex = b;
p->nextarc = G[a];    // 头插入
G[a] = p;

p = (ArcNode *)malloc(sizeof(ArcNode));
if (p == NULL) {
printf("OVERFLOW!\n");
exit(-1);
}
p->adjvex = a;
p->nextarc = G[b];    // 头插入
G[b] = p;
}
}

void Display(ArcNode *G[VERTEX_NUM + 1])
{
int i;
ArcNode *p;
for (i = 1; i <= VERTEX_NUM; i++) {
printf("%d", i);
for (p = G[i]; p != NULL; p = p->nextarc) {
printf("->%d", p->adjvex);
}
printf("\n");
}
}

void Free(ArcNode *G[VERTEX_NUM + 1])
{
int i;
ArcNode *p;
ArcNode *q;
for (i = 1; i <= VERTEX_NUM; i++) {
for (p = G[i]; p != NULL;) {
q = p;
p = p->nextarc;
free(q);
q = NULL;
}
}
}

int main(int argc, char **argv)
{
// 头结点数组设为指针数组
ArcNode *G[VERTEX_NUM + 1] = {NULL};    // 若这句放到freopen下面则错误，C语言！
freopen("cin.txt", "r", stdin);

CreatAdjListGraph(G);    // 建图（邻接表表示）

Display(G);                // 显示图

BFSTraverse(G);         // 遍历图

Free(G);                // 释放图

return 0;
}

/* cin.txt:
1 2
2 4
2 5
8 4
8 5
1 3
3 6
3 7
6 7
0 0
*/