684. Redundant Connection

本文探讨了在一个原本为树形结构的图中,如何通过使用并查集(Disjoint Sets)算法找出额外添加的一条边,该边导致图中出现环。并查集是一种用于处理不相交集合的高效数据结构,适用于解决此类图论问题。

摘要生成于 C知道 ,由 DeepSeek-R1 满血版支持, 前往体验 >

Description

In this problem, a tree is an undirected graph that is connected and has no cycles.

The given input is a graph that started as a tree with N nodes (with distinct values 1, 2, …, N), with one additional edge added. The added edge has two different vertices chosen from 1 to N, and was not an edge that already existed.

The resulting graph is given as a 2D-array of edges. Each element of edges is a pair [u, v] with u < v, that represents an undirected edge connecting nodes u and v.

Return an edge that can be removed so that the resulting graph is a tree of N nodes. If there are multiple answers, return the answer that occurs last in the given 2D-array. The answer edge [u, v] should be in the same format, with u < v.

Example 1:
Input: [[1,2], [1,3], [2,3]]
Output: [2,3]
Explanation: The given undirected graph will be like this:
1
/
2 - 3
Example 2:
Input: [[1,2], [2,3], [3,4], [1,4], [1,5]]
Output: [1,4]
Explanation: The given undirected graph will be like this:
5 - 1 - 2
| |
4 - 3
Note:
The size of the input 2D-array will be between 3 and 1000.
Every integer represented in the 2D-array will be between 1 and N, where N is the size of the input array.

Update (2017-09-26):
We have overhauled the problem description + test cases and specified clearly the graph is an undirected graph. For the directed graph follow up please see Redundant Connection II). We apologize for any inconvenience caused.

Problem URL


Solution

给一个图,有N个节点,labeled from 1 to N。本来是一棵树,但是现在多了一条边,找到多的这条边。

We could maintain a parent array to denote the parent of a connected component. An edge will connect two nodes into one connected component.

When we count an edge in, if the two nodes have already been in the same connected component, the edge will result in a cycle. That is, the edge is redundant.

We can make use of Disjoint Sets (Union Find).
If we regard a node as an element, a connected component is actually a disjoint set.

Code
class Solution {
    public int[] findRedundantConnection(int[][] edges) {
        int[] parents = new int[edges.length + 1];
        for (int[] edge: edges){
            if (find(parents, edge[0]) == find(parents, edge[1])){
                return edge;
            }
            else{
                parents[find(parents, edge[0])] = find(parents, edge[1]);
            }
        }
        return new int[2];
    }
    
    private int find (int[] parents, int n){
        if (parents[n] == 0){
            return n;
        }
        else{
            return find(parents, parents[n]);
        }
    }
}

Time Complexity: O()
Space Complexity: O()


Review
评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值