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// stdafx.h : 标准系统包含文件的包含文件，// 或是经常使用但不常更改的// 特定于项目的包含文件//#pragma once#include "targetver.h"#include <stdio.h>#include <tchar.h>#include<iostream>#include<string>#include<vector>#include<cmath>#include<map>#include<set>#include<algorithm>#include<iterator>#include<unordered_map>#include<iomanip>#include<typeinfo>// TODO: 在此处引用程序需要的其他头文件

// aiqiyi.cpp: 定义控制台应用程序的入口点。//#include "stdafx.h"using namespace std;int times = 0;class Node{public:	int val;	Node* parent;	vector<Node*> next;	int color;	int start_time;	int end_time;	Node(int val_char, Node* par, vector<Node*> nex, int col, int sta_t, int end_t) :		val(val_char), parent(par), next(nex), color(col), start_time(sta_t), end_time(end_t) {}};void DFS_VISIT(vector<vector<Node*>>& node_next, vector<Node*>& node_set, int target){	times++;	node_set[target]->start_time = times;	node_set[target]->color = 1;	for (int i = 0; i < node_next[target].size(); ++i)	{		if ((node_next[target][i])->color == 0)		{			(node_next[target][i])->parent = node_set[target];			DFS_VISIT(node_next, node_set, node_next[target][i]->val-'q');		}	}	times++;	node_set[target]->end_time = times;}void DFS(vector<vector<Node*>>& node_next, vector<Node*>& node_set){	for (int i = 0; i < 10; ++i)	{		if ((node_set[i])->color == 0)			DFS_VISIT(node_next, node_set, i);	}}int main(){	vector<vector<Node*> >node_next(10,vector<Node*>(0));	vector<Node*> node_set;	for (int i = 0; i < 10; ++i)	{		auto temp = new Node('q' + i, NULL, node_next[i], 0, 0, 0);		node_set.push_back(temp);	}	(node_next[0]).push_back(node_set[2]);	(node_next[0]).push_back(node_set[3]);	(node_next[0]).push_back(node_set[6]);	(node_next[1]).push_back(node_set[4]);	(node_next[1]).push_back(node_set[8]);	(node_next[2]).push_back(node_set[5]);	(node_next[3]).push_back(node_set[7]);	(node_next[3]).push_back(node_set[8]);	(node_next[4]).push_back(node_set[8]);	(node_next[5]).push_back(node_set[6]);	node_next[6].push_back(node_set[2]);	(node_next[7]).push_back(node_set[9]);	(node_next[8]).push_back(node_set[0]);	(node_next[9]).push_back(node_set[7]);	DFS(node_next,node_set);	for (int i = 0; i < 10; i++)		cout << node_set[i]->start_time<<" "<<node_set[i]->end_time << endl;	return 0;}

void DFS_noncursion(vector<vector<Node*>>& node_next, vector<Node*>& node_set){	stack<Node*> node_stack;	node_stack.push(node_set[0]);	int iter = 0;	while (iter < 10)	{		if (node_stack.empty())		{			while (iter < 10 && node_set[iter]->color)				++iter;			if (iter >= 10)				break;			node_stack.push(node_set[iter]);		}		else		{			while (!node_stack.empty())			{				auto top_rank = (node_stack.top())->val;				if (node_set[top_rank - 'q']->color == 0)				{					times++;					node_set[top_rank - 'q']->start_time = times;					node_set[top_rank - 'q']->color = 1;				}				int sign = 1;				for (int j = 0; j < node_next[top_rank - 'q'].size(); ++j)				{					if (node_next[top_rank - 'q'][j]->color == 0)					{						cout << char(node_next[top_rank - 'q'][j]->val) << endl;						node_next[top_rank - 'q'][j]->parent = node_set[top_rank - 'q'];						node_stack.push(node_next[top_rank - 'q'][j]);						sign = 0;						break;					}				}				if (sign)				{					times++;					node_set[top_rank - 'q']->end_time = times;					node_stack.pop();				}			}		}	}}

以下为尝试用CLRS上的DFS与拓扑排序检查有向图中是否存在环。

// aiqiyi.cpp: 定义控制台应用程序的入口点。  //  #include "stdafx.h"  using namespace std;static int times = 0;static bool sign = 0;class Node{public:	int val;	int parent;	vector<Node*> next;	int color;	int start_time;	int end_time;	Node(int val_char, int par, vector<Node*> nex, int col, int sta_t, int end_t) :		val(val_char), parent(par), next(nex), color(col), start_time(sta_t), end_time(end_t) {}};int find_index(vector<Node*>& node_set, int targets){	for (int ind = 0; ind < node_set.size(); ++ind)	{		if (node_set[ind]->val == targets)			return ind;	}}int DFS_VISIT(vector<vector<Node*>> node_next, vector<Node*> node_set, int targets)//targets is the value of node!!{	times++;	int target = find_index(node_set, targets);	node_set[target]->start_time = times;	node_set[target]->color = 1;	for (int i = 0; i < node_next[target].size(); ++i)	{		if ((node_next[target][i])->color == 0)		{			if (sign)				return 1;			(node_next[target][i])->parent = node_set[target]->val;			DFS_VISIT(node_next, node_set, node_next[target][i]->val);		}	}	times++;	node_set[target]->end_time = times;	return 0;}int DFS(vector<vector<Node*>> node_next, vector<Node*> node_set){	for (int i = 0; i < node_set.size(); ++i)	{		if ((node_set[i])->color == 0)		{			if (DFS_VISIT(node_next, node_set, node_set[i]->val))				return 1;		}	}	return 0;}static const bool Less(const int &a, const int & b){	return a >= b;}bool canFinish(int numCourses, vector<pair<int, int>>& prerequisites){	vector<vector<Node*> >node_next(numCourses, vector<Node*>(0));	vector<Node*> node_set;	vector<vector<Node*> >node_next_T(numCourses, vector<Node*>(0));	vector<Node*> node_set_T;	for (int i = 0; i < numCourses; ++i)	{		auto temp = new Node(i, 0, node_next[i], 0, 0, 0);		auto temp_T = new Node(i, 0, node_next_T[i], 0, 0, 0);;		node_set.push_back(temp);		node_set_T.push_back(temp_T);	}	int pair_len = prerequisites.size();	for (int i = 0; i < pair_len; ++i)//to generate the graph	{		node_next[prerequisites[i].first].push_back(node_set[prerequisites[i].second]);		node_next_T[prerequisites[i].second].push_back(node_set_T[prerequisites[i].first]);	}	for (int i = 0; i < numCourses; ++i)	{		node_set[i]->next = node_next[i];		node_set_T[i]->next = node_next_T[i];	}	//we need to check if it's an DAG first--to check if there exists a strongly-connectedly-component	DFS(node_next,node_set);		//to record the finish time of each node_visit in the first round of DFS;the info is useful for the next round DFS	vector<int>fin_time;	for (int i = 0; i < numCourses; ++i)		fin_time.push_back(node_set[i]->end_time);	//release memory!!!	vector<Node*>().swap(node_set);	vector<vector<Node*>>().swap(node_next);	//to compare the vector before and after sort, then you'll know the rank of numbers in the vector	//here maybe you can use priority queue	vector<int>fin_time_I = fin_time;	sort(fin_time.begin(), fin_time.end(),Less);	vector<int>index;	for (int i = 0; i < numCourses; ++i)	{		index.push_back(find(fin_time_I.begin(),fin_time_I.end(),fin_time[i])-fin_time_I.begin());	}	//sort node_set_T and node_next_T in the visiting order 	vector<vector<Node*> >node_next_R;	vector<Node*>node_set_R;	for (int i = 0; i < numCourses; ++i)	{		node_set_R.push_back(node_set_T[index[i]]);		node_next_R.push_back(node_next_T[index[i]]);	}	sign = 1;	times = 0;	int res = !DFS(node_next_R, node_set_R);	//for (int i = 0; i < numCourses; ++i)	//{	//	cout <<"node_num:"<< node_set_R[i]->val<<" sta:"<< node_set_R[i]->start_time<<" end:"<<node_set_R[i]->end_time << endl;	//}	for (int i = 0; i < numCourses; ++i)		delete node_set_T[i];	vector<Node*>().swap(node_set_T);	vector<Node*>().swap(node_set_R);	vector<vector<Node*>>().swap(node_next_T);	vector<vector<Node*>>().swap(node_next_R);	return res;}int main(){	vector<pair<int, int>> pre;	//pre.push_back({ 2,1 });	pre.push_back({ 1,0 });	//pre.push_back({ 0,2 });	cout<<canFinish(2, pre)<<endl;	return 0;}

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