餓...Course中的某題...DAG

由於涉及了一個比較常用的算法，用拓撲排序判斷一個有向圖是否無環，因此mark下來

#include <iostream>
#include <memory.h>
#include <vector>
#include <stack>

using namespace std;

const int MAX = 1000;

bool graph[MAX][MAX];
bool visited[MAX];
int inDegree[MAX];
bool ifRing = false;
stack<int> zeroInDegreeVertex;

void topologicalSort(int nodeNum, int edgeNum)
{
	vector<int> sortElements;
	int topNode;

	int edges = edgeNum;

	while (!zeroInDegreeVertex.empty())
	{
		topNode = zeroInDegreeVertex.top();
		zeroInDegreeVertex.pop();
		sortElements.push_back(topNode);
		for (int i = 1; i <= nodeNum; i++)
		{
			if (graph[topNode][i])
			{
				graph[topNode][i] = false;
				inDegree[i]--;
				edges--;
				if (inDegree[i] == 0)
				{
					zeroInDegreeVertex.push(i);
				}
			}
		}
	}
	
	if (edges > 0)
	{
		ifRing = true;
	}
	else
	{
		ifRing = false;
	}

	for (int i = 0; i < sortElements.size(); i++)
	{
		cout << sortElements[i] << " ";
	}
	cout << endl << endl;

}

int main()
{
	int nodeNum;
	int edgeNum;

	int start;
	int end;

	bool flag = false;

	memset(graph, false, sizeof(graph));
	memset(visited, false, sizeof(visited));
	memset(inDegree, 0, sizeof(inDegree));
	visitedNodeNum = 0;

	cin >> nodeNum >> edgeNum;

	for (int i = 0; i < edgeNum; i++)
	{
		cin >> start >> end;
		graph[start][end] = true;
		inDegree[end]++;
	}

	for (int i = 1; i <= nodeNum; i++)
	{
		if (inDegree[i] == 0)
		{
			zeroInDegreeVertex.push(i);
		}
	}

	topologicalSort(nodeNum, edgeNum);

	if (ifRing == true)
		cout << "0" << endl;
	else
		cout << "1" << endl; 

	return 0;
}