# Leetcode Course Schedule problem solution

In this Leetcode Course Schedule problem solution, There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array of prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai.

For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.

Return true if you can finish all courses. Otherwise, return false.

## Problem solution in Python.

```def canFinish(self, numCourses, prerequisites):
def cycle(v, G, R, B):
if v in R: return True
if v in G:
for _v in G[v]:
if _v not in B and cycle(_v, G, R, B): return True
return False

G, R, B = collections.defaultdict(list), set(), set()
for p in prerequisites:
G[p[0]].append(p[1])
for v in G:
if v not in B and cycle(v, G, R, B): return False
return True
```

## Problem solution in Java.

```public boolean canFinish(int numCourses, int[][] prerequisites) {
if (prerequisites == null || prerequisites.length == 0) return true;
int n = numCourses;
int[] vis = new int[n];
Map<Integer, List<Integer>> map = new HashMap<>();
for (int i = 0; i < n; ++i) map.put(i, new ArrayList<Integer>());
for (int[] p : prerequisites) {
}
for (int i = 0; i < n; ++i) {
if (!dfs(i, vis, map)) return false;
}
return true;
}

private boolean dfs(int i, int[] vis, Map<Integer, List<Integer>> map) {
if (vis[i] == 1) return false;
if (vis[i] == 2) return true;
vis[i] = 1;
for (int next : map.get(i)) {
if (!dfs(next, vis, map)) return false;
}
vis[i] = 2;
return true;
}
```

## Problem solution in C++.

```#define x a[i]
#define first x[0]
#define second x[1]
#define pb push_back
#define f q.front()
bool canFinish(int n, vector<vector<int>>& a) {
queue<int> q;
for(i=0;i<a.size();i++)
{
q.push(second);
while(!q.empty())
{
if(f==first) return 0;
q.pop();
}
}
return 1;
}
```

## Problem solution in C.

```struct adjnode{
int dep;
};
};
struct graph{
int v;
};
struct graph* create(int num){
struct graph *g = (struct graph *)malloc(sizeof(struct graph));
g->v = num;
for(int i=0;i<num;i++){
}
return g;
}
void add_edge(struct graph *g, int src, int dest){
new->dep = dest;
}

bool iscyclic(struct graph *g, bool *visited, bool *restack, int v){
if (visited[v] == false){
visited[v] = true;
restack[v] = true;
while (cur){
if (!visited[cur->dep] && iscyclic(g,visited,restack,cur->dep))
return true;
else if (restack[cur->dep]==true)
return true;
cur = cur->next;
}
}
restack[v] = false;
return false;
}
bool canFinish(int numCourses, int** prerequisites, int prerequisitesRowSize, int prerequisitesColSize) {
struct graph *g = create(numCourses);
int i;
for (i=0;i<prerequisitesRowSize;i++){
}
bool visited[numCourses];
bool restack[numCourses];
for(i=0;i<numCourses;i++){
visited[i] = false;
restack[i] = false;
}
for(i=0;i<numCourses;i++){
if(iscyclic(g,&visited[0], &restack[0],i))
return false;
}
return true;
}
```
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