t.elem=(int*)malloc(5*sizeof(int))
时间: 2023-11-21 22:05:20 浏览: 35
This code allocates memory dynamically for an array of 5 integers and assigns the address of the first element to the pointer variable t.elem.
In other words, t.elem is now pointing to a block of memory that can hold 5 integers, and we can access each element using array notation like t.elem[0], t.elem[1], t.elem[2], t.elem[3], and t.elem[4].
This is useful when we want to create an array whose size is not known at compile-time, or when we want to allocate memory on the heap instead of the stack.
However, it's important to remember to free the memory when we're done using it to avoid memory leaks. We can do this by calling free(t.elem).
相关问题
#include "stdio.h" #include "stdlib.h" #include "malloc.h" #define Null 0 #define MAX 20 typedef struct ArcNode { int adjvex; int weight; struct ArcNode *nextarc; }ArcNode,*AdjList; typedef struct Graph { AdjList elem[MAX+1]; int vexnum; int arcnum; int GraphKind; }Graph; typedef struct Stack { int s[MAX]; int top; }Stack; void initStack(Stack *s) { (*s).top=0; } int Push(Stack *s, int e) { if((*s).top>=MAX) return 0; else (*s).s[(*s).top++]=e; } int Pop(Stack *s, int *e) { if((*s).top<=0) return 0; else *e=(*s).s[--(*s).top]; } int StackEmpty(Stack s) { if(s.top==0)return 1; else return 0; } void create(Graph *G) { int i, start, end; AdjList p; for(i=0;i<=MAX;i++) (*G).elem[i]=Null; for(i=1;i<=(*G).arcnum;i++) { scanf("%d,%d",&start,&end); p=(AdjList)malloc(sizeof(ArcNode)); p->adjvex=end; p->nextarc=(*G).elem[start]; (*G).elem[start]=p; if((*G).GraphKind==0) { p=(AdjList)malloc(sizeof(ArcNode)); p->adjvex=start; p->nextarc=(*G).elem[end]; (*G).elem[end]=p; } } } int TopoSort(Graph G) { } main() { Graph G; printf("Please input the number of vex, arc and GraphKind:"); scanf("%d,%d,%d",&G.vexnum,&G.arcnum,&G.GraphKind); create(&G); printf("The outcome of TopoSort is:\n"); TopoSort(G); }
这段代码是一个基于邻接表存储结构的有向图的拓扑排序的程序框架。但是其中的 TopoSort 函数还没有实现,需要我们来完成。
拓扑排序的算法是基于 Kahn 算法的。其基本思想是不断地选择入度为 0 的顶点,并将其从图中删除,直到所有顶点都被选择为止。在实现过程中,我们需要使用一个队列来存储入度为 0 的顶点。
在这个程序中,我们可以将入度为 0 的顶点入栈,然后依次出栈并处理它们的邻接节点,更新它们的入度。具体实现细节可以参考下面的代码。
```c
int TopoSort(Graph G) {
int i, e, cnt = 0;
int *indegree = (int *)malloc(sizeof(int) * (G.vexnum + 1));
Stack s;
initStack(&s);
for (i = 1; i <= G.vexnum; i++) {
indegree[i] = 0;
}
for (i = 1; i <= G.vexnum; i++) {
AdjList p = G.elem[i];
while (p != Null) {
indegree[p->adjvex]++;
p = p->nextarc;
}
}
for (i = 1; i <= G.vexnum; i++) {
if (indegree[i] == 0) {
Push(&s, i);
}
}
while (!StackEmpty(s)) {
Pop(&s, &e);
printf("%d ", e);
cnt++;
AdjList p = G.elem[e];
while (p != Null) {
indegree[p->adjvex]--;
if (indegree[p->adjvex] == 0) {
Push(&s, p->adjvex);
}
p = p->nextarc;
}
}
if (cnt != G.vexnum) {
printf("Error: the graph has a cycle.\n");
return 0;
}
return 1;
}
```
上面的代码实现了基于邻接表存储结构的有向图的拓扑排序。其中使用了一个栈来存储入度为 0 的顶点,使用了一个数组来存储每个顶点的入度。如果拓扑排序成功,会输出拓扑排序序列;如果图中存在环,会输出错误信息。
完整的程序如下:
```c
#include "stdio.h"
#include "stdlib.h"
#include "malloc.h"
#define Null 0
#define MAX 20
typedef struct ArcNode {
int adjvex;
int weight;
struct ArcNode *nextarc;
} ArcNode, *AdjList;
typedef struct Graph {
AdjList elem[MAX + 1];
int vexnum;
int arcnum;
int GraphKind;
} Graph;
typedef struct Stack {
int s[MAX];
int top;
} Stack;
void initStack(Stack *s) {
(*s).top = 0;
}
int Push(Stack *s, int e) {
if ((*s).top >= MAX)
return 0;
else
(*s).s[(*s).top++] = e;
}
int Pop(Stack *s, int *e) {
if ((*s).top <= 0)
return 0;
else
*e = (*s).s[--(*s).top];
}
int StackEmpty(Stack s) {
if (s.top == 0)
return 1;
else
return 0;
}
void create(Graph *G) {
int i, start, end;
AdjList p;
for (i = 0; i <= MAX; i++)
(*G).elem[i] = Null;
for (i = 1; i <= (*G).arcnum; i++) {
scanf("%d,%d", &start, &end);
p = (AdjList) malloc(sizeof(ArcNode));
p->adjvex = end;
p->nextarc = (*G).elem[start];
(*G).elem[start] = p;
if ((*G).GraphKind == 0) {
p = (AdjList) malloc(sizeof(ArcNode));
p->adjvex = start;
p->nextarc = (*G).elem[end];
(*G).elem[end] = p;
}
}
}
int TopoSort(Graph G) {
int i, e, cnt = 0;
int *indegree = (int *) malloc(sizeof(int) * (G.vexnum + 1));
Stack s;
initStack(&s);
for (i = 1; i <= G.vexnum; i++) {
indegree[i] = 0;
}
for (i = 1; i <= G.vexnum; i++) {
AdjList p = G.elem[i];
while (p != Null) {
indegree[p->adjvex]++;
p = p->nextarc;
}
}
for (i = 1; i <= G.vexnum; i++) {
if (indegree[i] == 0) {
Push(&s, i);
}
}
while (!StackEmpty(s)) {
Pop(&s, &e);
printf("%d ", e);
cnt++;
AdjList p = G.elem[e];
while (p != Null) {
indegree[p->adjvex]--;
if (indegree[p->adjvex] == 0) {
Push(&s, p->adjvex);
}
p = p->nextarc;
}
}
if (cnt != G.vexnum) {
printf("Error: the graph has a cycle.\n");
return 0;
}
return 1;
}
int main() {
Graph G;
printf("Please input the number of vex, arc and GraphKind:");
scanf("%d,%d,%d", &G.vexnum, &G.arcnum, &G.GraphKind);
create(&G);
printf("The outcome of TopoSort is:\n");
TopoSort(G);
return 0;
}
```
#include "stdio.h"#include "stdlib.h"#include "malloc.h"#define Null 0#define MAX 20typedef struct ArcNode{int adjvex;int weight;struct ArcNode *nextarc;}ArcNode,*AdjList;typedef struct Graph{AdjList elem[MAX+1];int vexnum;int arcnum;int GraphKind;}Graph;typedef struct Stack{int s[MAX];int top;}Stack;void initStack(Stack *s){(*s).top=0;}int Push(Stack *s, int e){if((*s).top>=MAX) return 0;else (*s).s[(*s).top++]=e;}int Pop(Stack *s, int *e){if((*s).top<=0) return 0;else *e=(*s).s[--(*s).top];}int StackEmpty(Stack s){if(s.top==0)return 1;else return 0;}void create(Graph *G){int i, start, end; AdjList p;for(i=0;i<=MAX;i++)(*G).elem[i]=Null;for(i=1;i<=(*G).arcnum;i++){scanf("%d,%d",&start,&end);p=(AdjList)malloc(sizeof(ArcNode));p->adjvex=end;p->nextarc=(*G).elem[start];(*G).elem[start]=p;if((*G).GraphKind==0){p=(AdjList)malloc(sizeof(ArcNode));p->adjvex=start;p->nextarc=(*G).elem[end];(*G).elem[end]=p;}}}int TopoSort(Graph G){}main(){Graph G;printf("Please input the number of vex, arc and GraphKind:");scanf("%d,%d,%d",&G.vexnum,&G.arcnum,&G.GraphKind);create(&G);printf("The outcome of TopoSort is:\n");TopoSort(G);}阅读并运行下面程序,补充拓扑排序算法,根据输入,输出有向图的拓扑排序序列。。
这段程序中,缺少拓扑排序算法的具体实现,需要补充。
拓扑排序算法的基本思想是通过不断地删除入度为0的顶点来构造拓扑序列。
具体地,可以使用队列来实现拓扑排序算法。首先,计算每个顶点的入度,将入度为0的顶点加入队列中。然后,不断从队列中取出顶点,并将其从图中删除,同时将与其相邻的顶点的入度减1。如果删除后某个顶点的入度变为0,则将其加入队列中。当队列为空时,所有顶点都已经被删除,此时的顺序即为拓扑序列。
下面给出实现拓扑排序的代码:
```
int TopoSort(Graph G){
int i, j, k;
int count = 0; // 记录已经输出的顶点数
int indegree[MAX+1]; // 记录每个顶点的入度
ArcNode *p;
Stack s;
initStack(&s);
for (i = 1; i <= G.vexnum; i++) {
indegree[i] = 0;
}
// 计算每个顶点的入度
for (i = 1; i <= G.vexnum; i++) {
p = G.elem[i];
while (p != Null) {
indegree[p->adjvex]++;
p = p->nextarc;
}
}
// 将入度为0的顶点加入栈中
for (i = 1; i <= G.vexnum; i++) {
if (indegree[i] == 0) {
Push(&s, i);
}
}
// 不断从栈中取出顶点,输出,并删除与其相邻的边
while (!StackEmpty(s)) {
Pop(&s, &i);
printf("%d ", i);
count++;
p = G.elem[i];
while (p != Null) {
j = p->adjvex;
indegree[j]--;
if (indegree[j] == 0) {
Push(&s, j);
}
p = p->nextarc;
}
}
if (count < G.vexnum) {
printf("Error: the graph has a cycle!\n");
return 0;
}
return 1;
}
```
在主函数中,调用 `TopoSort` 函数即可完成拓扑排序。