> For the complete documentation index, see [llms.txt](https://junnie.gitbook.io/nine-chapter/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://junnie.gitbook.io/nine-chapter/10.-graph/1192.-critical-connections-in-a-network-h.md).

# 1192. Critical Connections in a Network (H)

There are `n` servers numbered from `0` to `n - 1` connected by undirected server-to-server `connections` forming a network where `connections[i] = [ai, bi]` represents a connection between servers `ai` and `bi`. Any server can reach other servers directly or indirectly through the network.

A *critical connection* is a connection that, if removed, will make some servers unable to reach some other server.

Return all critical connections in the network in any order.

 

**Example 1:**

![](https://assets.leetcode.com/uploads/2019/09/03/1537_ex1_2.png)

```
Input: n = 4, connections = [[0,1],[1,2],[2,0],[1,3]]
Output: [[1,3]]
Explanation: [[3,1]] is also accepted.
```

**Example 2:**

```
Input: n = 2, connections = [[0,1]]
Output: [[0,1]]
```

 

**Constraints:**

* `2 <= n <= 105`
* `n - 1 <= connections.length <= 105`
* `0 <= ai, bi <= n - 1`
* `ai != bi`
* There are no repeated connections.

### Solution:

<https://www.jiuzhang.com/problem/critical-connections-in-a-network/>\
DFS，graph中环的每条边都不是critical connections

通过看Youtube频道"小小福LeetCode" <https://www.youtube.com/watch?v=mKUsbABiwBI>的解释后写的Java代码

整体的思路就是， 把带环的删掉， 剩下的就是关键链接。 具体方法就是， 用dfs的层级来代表啥时候visit过， 如果发现之前就visit过， 那么说明有环， 把整个环删掉。 并且整个环都要知道下最小的那个depth在哪里<br>