LeetCode 1791. Find Center of Star Graph

Description

https://leetcode.com/problems/find-center-of-star-graph/

There is an undirected star graph consisting of n nodes labeled from 1 to n. A star graph is a graph where there is one center node and exactly n - 1 edges that connect the center node with every other node.

You are given a 2D integer array edges where each edges[i] = [ui, vi] indicates that there is an edge between the nodes ui and vi. Return the center of the given star graph.

Example 1:

Input: edges = [[1,2],[2,3],[4,2]]
Output: 2
Explanation: As shown in the figure above, node 2 is connected to every other node, so 2 is the center.

Example 2:

Input: edges = [[1,2],[5,1],[1,3],[1,4]]
Output: 1

Constraints:

  • 3 <= n <= 105
  • edges.length == n - 1
  • edges[i].length == 2
  • 1 <= ui, vi <= n
  • ui != vi
  • The given edges represent a valid star graph.

Explanation

Find the vertice which occurs the same as the number of edges.

Python Solution

class Solution:
    def findCenter(self, edges: List[List[int]]) -> int:
        
        counter = {}
        
        for edge in edges:
            counter[edge[0]] = counter.get(edge[0], 0) + 1
            counter[edge[1]] = counter.get(edge[1], 0) + 1
            
            
        for key, value in counter.items():
            if value == len(edges):
                return key
        
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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