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207.course-schedule.cpp
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207.course-schedule.cpp
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/*
* @lc app=leetcode id=207 lang=cpp
*
* [207] Course Schedule
*/
#include <unordered_map>
#include <vector>
using namespace std;
class Solution {
public:
vector<int> parent;
vector<vector<int>> G;
vector<bool> visited;
bool DFS(int vertex)
{
visited[vertex] = true;
int n = G[vertex].size();
for (int i = 0;i < n; i++)
{
int pre = G[vertex][i];
if (!visited[pre])
{
parent[pre] = vertex;
if (!DFS(pre))
return false;
}
else
{
int p = parent[vertex];
while (p != -1)
{
if (p == pre)
return false;
p = parent[p];
}
}
}
return true;
}
bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
G.resize(numCourses);
int n = prerequisites.size();
for (int i = 0;i < n; i++)
G[prerequisites[i][0]].push_back(prerequisites[i][1]);
visited.resize(numCourses);
parent.resize(numCourses, -1);
for (int i = 0;i < numCourses; i++)
if (!visited[i])
if (!DFS(i))
return false;
return true;
}
};