第一行输入有向图的顶点数和边的条数，以空格隔开

第二行输入每个顶点的数据，中间没有空格

第三行输入每条边，每条边的格式为i j，中间有空格，所有边占一行

第四行输入某个顶点的序号

输出要求顶点的入度，占一行

5 5
abcde
0 1 0 2 0 3 1 2 1 4
2

2

思路：全局变量计数器

通关代码：

#include<iostream>#define MAXSIZE 100using namespace std;//定义标记表
int visited[MAXSIZE] = { 0 };//入度计数器
int countInDegree = 0;//定义边表结点
struct EdgeNode
{int verSubscript;EdgeNode* next;
};
//定义顶点表结点
struct VertextNode
{char vertex;EdgeNode* edgeHead;
};class adjacencyList
{
public:adjacencyList(string str, int n, int e);~adjacencyList();
public:void calculateOutDegree(int v);void calculateInDegree(int v,int sub);
private:VertextNode vertexList[MAXSIZE];int vertextNum, edgeNum;
};adjacencyList::adjacencyList(string str, int n, int e)
{vertextNum = n;edgeNum = e;for (int i = 0; i < n; i++){vertexList[i].vertex = str[i];vertexList[i].edgeHead = NULL;}EdgeNode* s = NULL;for (int k = 0; k < edgeNum; k++){int i, j;cin >> i >> j;s = new EdgeNode;s->verSubscript = j;//注意边表中数据存的是下标s->next = vertexList[i].edgeHead;vertexList[i].edgeHead = s;}
}adjacencyList::~adjacencyList()
{EdgeNode* p = NULL, * q = NULL;for (int i = 0; i < vertextNum; i++){p = q = vertexList[i].edgeHead;while (p != NULL){p = p->next;delete q;q = p;}}
}//计算出度
void adjacencyList::calculateOutDegree(int v)
{int count = 0;EdgeNode* p = NULL;p = vertexList[v].edgeHead;while (p != NULL){count++;p = p->next;}cout << count;
}//计算入度
void adjacencyList::calculateInDegree(int v,int sub)
{EdgeNode* p = NULL;p = vertexList[v].edgeHead;while (p != NULL){int j = p->verSubscript;if (visited[j] == 0){if (j == sub)countInDegree++;calculateInDegree(j, sub);}p = p->next;}
}int main()
{string s;int n,e,sub;cin>>n>>e;cin>>s;adjacencyList adj(s, n, e);cin>>sub;adj.calculateInDegree(0,sub);cout<<countInDegree;return 0;
}