在头文件ljb.h中，更改头结点类型VertexNode（原头结点类型定义如下示），增加一个id数据域，用于标记结点的入度；编写一个函数void inDegree(LinkedGraph *g)，用于计算有向图中每个结点的入度。编写主函数验证该函数的正确性。文件名称：computerInDegree.c

修改后的头文件ljb.h：

#define MAX_VERTEX_NUM 20

typedef enum {DG, DN, UDG, UDN} GraphKind;

typedef struct ArcNode{
    int adjvex;
    struct ArcNode *nextarc;
    // 增加一个权值域
    int weight;
}ArcNode;

typedef struct VertexNode{
    char data;
    // 增加一个 id 数据域
    int id;
    ArcNode *firstarc;
}VertexNode, AdjList[MAX_VERTEX_NUM];

typedef struct{
    AdjList vertices;
    int vexnum, arcnum;
    GraphKind kind;
}LinkedGraph;

computerInDegree.c：

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

void inDegree(LinkedGraph *g) {
    // 初始化入度为 0
    int indegree[g->vexnum];
    for (int i = 0; i < g->vexnum; i++) {
        indegree[i] = 0;
    }
    // 遍历邻接表，计算每个结点的入度
    for (int i = 0; i < g->vexnum; i++) {
        ArcNode *p = g->vertices[i].firstarc;
        while (p != NULL) {
            indegree[p->adjvex]++;
            p = p->nextarc;
        }
    }
    // 输出每个结点的入度
    for (int i = 0; i < g->vexnum; i++) {
        printf("Vertex %c (id: %d) has in-degree: %d\n", g->vertices[i].data, g->vertices[i].id, indegree[i]);
    }
}

int main() {
    LinkedGraph g;
    // 构造图
    g.vexnum = 5;
    g.arcnum = 7;
    g.kind = DG;
    g.vertices[0].data = 'A';
    g.vertices[0].id = 0;
    g.vertices[0].firstarc = NULL;
    g.vertices[1].data = 'B';
    g.vertices[1].id = 1;
    g.vertices[1].firstarc = NULL;
    g.vertices[2].data = 'C';
    g.vertices[2].id = 2;
    g.vertices[2].firstarc = NULL;
    g.vertices[3].data = 'D';
    g.vertices[3].id = 3;
    g.vertices[3].firstarc = NULL;
    g.vertices[4].data = 'E';
    g.vertices[4].id = 4;
    g.vertices[4].firstarc = NULL;
    ArcNode *a1 = (ArcNode*)malloc(sizeof(ArcNode));
    a1->adjvex = 1;
    a1->weight = 1;
    a1->nextarc = g.vertices[0].firstarc;
    g.vertices[0].firstarc = a1;
    ArcNode *a2 = (ArcNode*)malloc(sizeof(ArcNode));
    a2->adjvex = 3;
    a2->weight = 1;
    a2->nextarc = g.vertices[0].firstarc;
    g.vertices[0].firstarc = a2;
    ArcNode *a3 = (ArcNode*)malloc(sizeof(ArcNode));
    a3->adjvex = 3;
    a3->weight = 1;
    a3->nextarc = g.vertices[1].firstarc;
    g.vertices[1].firstarc = a3;
    ArcNode *a4 = (ArcNode*)malloc(sizeof(ArcNode));
    a4->adjvex = 2;
    a4->weight = 1;
    a4->nextarc = g.vertices[2].firstarc;
    g.vertices[2].firstarc = a4;
    ArcNode *a5 = (ArcNode*)malloc(sizeof(ArcNode));
    a5->adjvex = 4;
    a5->weight = 1;
    a5->nextarc = g.vertices[2].firstarc;
    g.vertices[2].firstarc = a5;
    ArcNode *a6 = (ArcNode*)malloc(sizeof(ArcNode));
    a6->adjvex = 3;
    a6->weight = 1;
    a6->nextarc = g.vertices[3].firstarc;
    g.vertices[3].firstarc = a6;
    ArcNode *a7 = (ArcNode*)malloc(sizeof(ArcNode));
    a7->adjvex = 4;
    a7->weight = 1;
    a7->nextarc = g.vertices[3].firstarc;
    g.vertices[3].firstarc = a7;
    // 计算每个结点的入度
    inDegree(&g);
    return 0;
}

输出结果：

Vertex A (id: 0) has in-degree: 0
Vertex B (id: 1) has in-degree: 1
Vertex C (id: 2) has in-degree: 1
Vertex D (id: 3) has in-degree: 3
Vertex E (id: 4) has in-degree: 2

可以看到，每个结点的入度都被正确地计算出来了。