**Physical Address**

304 North Cardinal St.

Dorchester Center, MA 02124

There are a total of `numCourses`

courses you have to take, labeled from `0`

to `numCourses - 1`

. You are given an array `prerequisites`

where `prerequisites[i] = [a`

indicates that you _{i}, b_{i}]**must** take course `b`

first if you want to take course _{i}`a`

._{i}

- 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`

.

**Example 1:**

```
Input: numCourses = 2, prerequisites = [[1,0]]
Output: true
Explanation: There are a total of 2 courses to take.
To take course 1 you should have finished course 0. So it is possible.
```

**Example 2:**

```
Input: numCourses = 2, prerequisites = [[1,0],[0,1]]
Output: false
Explanation: There are a total of 2 courses to take.
To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.
```

**Constraints:**

`1 <= numCourses <= 2000`

`0 <= prerequisites.length <= 5000`

`prerequisites[i].length == 2`

`0 <= a`

_{i}, b_{i}< numCourses- All the pairs prerequisites[i] are
**unique**.

```
public boolean canFinish(int n, int[][] prerequisites) {
ArrayList<Integer>[] G = new ArrayList[n];
int[] degree = new int[n];
ArrayList<Integer> bfs = new ArrayList();
for (int i = 0; i < n; ++i) G[i] = new ArrayList<Integer>();
for (int[] e : prerequisites) {
G[e[1]].add(e[0]);
degree[e[0]]++;
}
for (int i = 0; i < n; ++i) if (degree[i] == 0) bfs.add(i);
for (int i = 0; i < bfs.size(); ++i)
for (int j: G[bfs.get(i)])
if (--degree[j] == 0) bfs.add(j);
return bfs.size() == n;
}
```

```
bool canFinish(int n, vector<vector<int>>& prerequisites) {
vector<vector<int>> G(n);
vector<int> degree(n, 0), bfs;
for (auto& e : prerequisites)
G[e[1]].push_back(e[0]), degree[e[0]]++;
for (int i = 0; i < n; ++i) if (!degree[i]) bfs.push_back(i);
for (int i = 0; i < bfs.size(); ++i)
for (int j: G[bfs[i]])
if (--degree[j] == 0) bfs.push_back(j);
return bfs.size() == n;
}
```

```
def canFinish(self, n, prerequisites):
G = [[] for i in range(n)]
degree = [0] * n
for j, i in prerequisites:
G[i].append(j)
degree[j] += 1
bfs = [i for i in range(n) if degree[i] == 0]
for i in bfs:
for j in G[i]:
degree[j] -= 1
if degree[j] == 0:
bfs.append(j)
return len(bfs) == n
```

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